chore: add markdown formatting and README.md

Author: simschla

README.md

@@ -0,0 +1,29 @@
+# <img align="left" src="../_images/spotless_logo.png"> Spotless Command Line Interface CLI
+
+_Keep your code Spotless with Gradle_
+
+<!---freshmark shields
+output = [
+  link(shield('Changelog', 'changelog', '{{versionLast}}', 'blue'), 'CHANGES.md'),
+  '',
+  link(shield('OS Win', 'OS', 'Windows', 'blueviolet'), 'README.md'),
+  link(shield('OS Linux', 'OS', 'Linux', 'blueviolet'), 'README.md'),
+  link(shield('OS macOS', 'OS', 'macOS', 'blueviolet'), 'README.md'),
+  ].join('\n');
+-->
+
+[![Changelog](https://img.shields.io/badge/changelog-versionLast%3DUNKNOWN-blue.svg)](CHANGES.md)
+
+[![OS Win](https://img.shields.io/badge/OS-Windows-blueviolet.svg)](README.md)
+[![OS Linux](https://img.shields.io/badge/OS-Linux-blueviolet.svg)](README.md)
+[![OS macOS](https://img.shields.io/badge/OS-macOS-blueviolet.svg)](README.md)
+
+<!---freshmark /shields -->
+
+`spotless` is a command line interface (CLI) for the [spotless code formatter](../README.md).
+It intends to be a simple alternative to its siblings: the plugins for [gradle](../plugin-gradle/README.md), [maven](../plugin-maven/README.md)
+and others.
+
+- TODO: add usage and examples
+- TBD: can usage be generated automatically e.g. via freshmark?
+-

build-logic/src/main/groovy/buildlogic.spotless-markdown-conventions.gradle

@@ -0,0 +1,11 @@
+plugins {
+    id 'buildlogic.spotless-common-conventions'
+}
+
+spotless {
+    freshmark { // freshmark for keeping markdown files up to date
+        target '*.md'
+        prettier() // prettier for markdown formatting
+    }
+
+}

build.gradle

@@ -1,5 +1,6 @@
 plugins {
 	id 'buildlogic.spotless-gradle-conventions'
+	id 'buildlogic.spotless-markdown-conventions'
 }
 
 subprojects {