1480: add configuration to readme

Author: simschla

plugin-gradle/README.md

@@ -67,7 +67,7 @@ Spotless supports all of Gradle's built-in performance features (incremental bui
   - [Javascript](#javascript) ([prettier](#prettier), [ESLint](#eslint-javascript))
   - [JSON](#json)
   - Multiple languages
-    - [Prettier](#prettier) ([plugins](#prettier-plugins), [npm detection](#npm-detection), [`.npmrc` detection](#npmrc-detection))
+    - [Prettier](#prettier) ([plugins](#prettier-plugins), [npm detection](#npm-detection), [`.npmrc` detection](#npmrc-detection), [caching `npm install` results](#caching-results-of-npm-install))
       - javascript, jsx, angular, vue, flow, typescript, css, less, scss, html, json, graphql, markdown, ymaml
     - [clang-format](#clang-format)
       - c, c++, c#, objective-c, protobuf, javascript, java
@@ -630,7 +630,8 @@ spotless {
 
 **Prerequisite: tsfmt requires a working NodeJS version**
 
-For details, see the [npm detection](#npm-detection) and [`.npmrc` detection](#npmrc-detection) sections of prettier, which apply also to tsfmt.
+For details, see the [npm detection](#npm-detection), [`.npmrc` detection](#npmrc-detection) and [caching results of `npm install`](#caching-results-of-npm-install) sections of prettier, which apply also to tsfmt.
+
 
 ### ESLint (Typescript)
 
@@ -678,7 +679,7 @@ spotless {
 
 **Prerequisite: ESLint requires a working NodeJS version**
 
-For details, see the [npm detection](#npm-detection) and [`.npmrc` detection](#npmrc-detection) sections of prettier, which apply also to ESLint.
+For details, see the [npm detection](#npm-detection), [`.npmrc` detection](#npmrc-detection) and [caching results of `npm install`](#caching-results-of-npm-install) sections of prettier, which apply also to ESLint.
 
 ## Javascript
 
@@ -742,7 +743,7 @@ spotless {
 
 **Prerequisite: ESLint requires a working NodeJS version**
 
-For details, see the [npm detection](#npm-detection) and [`.npmrc` detection](#npmrc-detection) sections of prettier, which apply also to ESLint.
+For details, see the [npm detection](#npm-detection), [`.npmrc` detection](#npmrc-detection) and [caching results of `npm install`](#caching-results-of-npm-install) sections of prettier, which apply also to ESLint.
 
 ## JSON
 
@@ -926,8 +927,6 @@ node- and npm-binaries dynamically installed by this plugin. See
 [this](https://github.com/diffplug/spotless/blob/main/plugin-gradle/src/test/resources/com/diffplug/gradle/spotless/NpmTestsWithoutNpmInstallationTest_gradle_node_plugin_example_1.gradle)
 or [this](https://github.com/diffplug/spotless/blob/main/plugin-gradle/src/test/resources/com/diffplug/gradle/spotless/NpmTestsWithoutNpmInstallationTest_gradle_node_plugin_example_2.gradle) example.
 
-```gradle
-
 ### `.npmrc` detection
 
 Spotless picks up npm configuration stored in a `.npmrc` file either in the project directory or in your user home.
@@ -940,6 +939,22 @@ spotless {
     prettier().npmrc("$projectDir/config/.npmrc").config(...)
 ```
 
+### Caching results of `npm install`
+
+Spotless uses `npm` behind the scenes to install `prettier`. This can be a slow process, especially if you are using a slow internet connection or
+if you need large plugins. You can instruct spotless to cache the results of the `npm install` calls, so that for the next installation,
+it will not need to download the packages again, but instead reuse the cached version.
+
+```gradle
+spotless {
+  typescript {
+    prettier().npmInstallCache() // will use the default cache directory (the build-directory of the respective module)
+    prettier().npmInstallCache("${rootProject.rootDir}/.gradle/spotless-npm-cache") // will use the specified directory (creating it if not existing)
+```
+
+Depending on your filesystem and the location of the cache directory, spotless will use hardlinks when caching the npm packages. If that is not
+possible, it will fall back to copying the files.
+
 ## clang-format
 
 [homepage](https://clang.llvm.org/docs/ClangFormat.html). [changelog](https://releases.llvm.org/download.html). `clang-format` is a formatter for c, c++, c#, objective-c, protobuf, javascript, and java. You can use clang-format in any language-specific format, but usually you will be creating a generic format.

plugin-maven/README.md

@@ -54,7 +54,7 @@ user@machine repo % mvn spotless:check
   - [JSON](#json)
   - [YAML](#yaml)
   - Multiple languages
-    - [Prettier](#prettier) ([plugins](#prettier-plugins), [npm detection](#npm-detection), [`.npmrc` detection](#npmrc-detection))
+    - [Prettier](#prettier) ([plugins](#prettier-plugins), [npm detection](#npm-detection), [`.npmrc` detection](#npmrc-detection), [caching `npm install` results](#caching-results-of-npm-install))
     - [eclipse web tools platform](#eclipse-web-tools-platform)
 - **Language independent**
   - [Generic steps](#generic-steps)
@@ -731,7 +731,7 @@ The auto-discovery of config files (up the file tree) will not work when using t
 
 **Prerequisite: tsfmt requires a working NodeJS version**
 
-For details, see the [npm detection](#npm-detection) and [`.npmrc` detection](#npmrc-detection) sections of prettier, which apply also to tsfmt.
+For details, see the [npm detection](#npm-detection), [`.npmrc` detection](#npmrc-detection) and [caching results of `npm install`](#caching-results-of-npm-install) sections of prettier, which apply also to tsfmt.
 
 ### ESLint (typescript)
 
@@ -787,7 +787,7 @@ reference to a `tsconfig.json` is required.
 
 **Prerequisite: ESLint requires a working NodeJS version**
 
-For details, see the [npm detection](#npm-detection) and [`.npmrc` detection](#npmrc-detection) sections of prettier, which apply also to ESLint.
+For details, see the [npm detection](#npm-detection), [`.npmrc` detection](#npmrc-detection) and [caching results of `npm install`](#caching-results-of-npm-install) sections of prettier, which apply also to ESLint.
 
 
 ## Javascript
@@ -863,7 +863,7 @@ The configuration is very similar to the [ESLint (Typescript)](#eslint-typescrip
 
 **Prerequisite: ESLint requires a working NodeJS version**
 
-For details, see the [npm detection](#npm-detection) and [`.npmrc` detection](#npmrc-detection) sections of prettier, which apply also to ESLint.
+For details, see the [npm detection](#npm-detection), [`.npmrc` detection](#npmrc-detection) and [caching results of `npm install`](#caching-results-of-npm-install) sections of prettier, which apply also to ESLint.
 
 ## JSON
 
@@ -1113,6 +1113,21 @@ Alternatively you can supply spotless with a location of the `.npmrc` file to us
   <npmrc>/usr/local/shared/.npmrc</npmrc>
 ```
 
+### Caching results of `npm install`
+
+Spotless uses `npm` behind the scenes to install `prettier`. This can be a slow process, especially if you are using a slow internet connection or
+if you need large plugins. You can instruct spotless to cache the results of the `npm install` calls, so that for the next installation,
+it will not need to download the packages again, but instead reuse the cached version.
+
+```xml
+<prettier>
+  <npmInstallCache>true</npmInstallCache> <!-- will use the default cache directory (the `target`-directory) -->
+  <npmInstallCache>/usr/local/shared/.spotless-npm-install-cache</npmInstallCache> <!-- will use the specified directory (creating it if not existing) -->
+```
+
+Depending on your filesystem and the location of the cache directory, spotless will use hardlinks when caching the npm packages. If that is not
+possible, it will fall back to copying the files.
+
 <a name="applying-eclipse-wtp-to-css--html--etc"></a>
 
 ## Eclipse web tools platform