doc: fix instructions for execution of tests

Author: adrienjoly

README.md

@@ -20,14 +20,26 @@ Summary:
 
 ## Installation, tests and CLI usage
 
+After installing [Node.js](https://nodejs.org/):
+
 ```sh
-nvm use # optional, to switch to the recommended version of Node.js
-npm install pdfreader
-cd node_modules/pdfreader
+git clone https://github.com/adrienjoly/npm-pdfreader.git
+cd npm-pdfreader
+npm install
 npm test
 node parse.js test/sample.pdf
 ```
 
+## Installation into an existing project
+
+To install `pdfreader` as a dependency of your Node.js project:
+
+```sh
+npm install pdfreader
+```
+
+Then, see below for examples of use.
+
 ## Raw PDF reading
 
 This module exposes the `PdfReader` class, to be instantiated. You can pass `{ debug: true }` to the constructor, in order to log debugging information. (useful for troubleshooting)