Update CONTRIBUTING.md

Author: cdujeu

CONTRIBUTING.md

@@ -19,3 +19,29 @@ PLEASE READ THE FOLLOWING BEFORE POSTING A BUG.
 **POST A GITHUB ISSUE / SUBMIT PR**
 > Make sure to put as many details as possible. If you are referring to a discussion on the Forum, add the link. The more info you give, the more easily we can reproduce the bug, the quicker we can fix it.  
 > If you are submitting a Pull Request, please sign the [Contributor License Agreement](https://pydio.com/en/community/contribute/contributor-license-agreement-cla).
+
+
+#### Setting up your dev environment
+
+Pydio 7 requires **PHP5.6** and upper. 
+
+The web root of the application is located in ***core/src/***. Create a virtual host to point to this folder, set up your webserver to use index.php as default page. This is generally done by default. 
+
+Pydio uses Composer and NPM to manage dependencies respectively in PHP and JS. It uses Grunt to build javascript sources. In order to start Pydio locally after a fresh `git clone`, you will first have to run these tools in both the core and in many plugins. 
+
+ - First install Composer (see https://getcomposer.org) and NPM (https://docs.npmjs.com/getting-started/installing-node)
+ - Install Grunt globally by running `npm install -g grunt-cli``
+ - Inside the core folder (under webroot, i.e. core/src/core/ from root of git repository), run `composer install`
+ - For each plugin that contains a composer.json file, run `composer install` as well.
+ - For each plugin tat contains a package.json file, run
+   - `npm install`
+   - `grunt`
+
+On a unix-based machine, this can be achieved by the following command (from the webroot directory):  
+```
+find . -maxdepth 5 -name Gruntfile.js -execdir bash -c "npm install && grunt" \;  
+find . -maxdepth 5 -name composer.json -execdir composer install \;
+```
+
+You should be good to go. When modifying JS files that require transpilation, there is generally a `grunt watch` task available to automatically run grunt on each file change.
+