Add information about contributing to the script

Issue: tiliado/nuvolaplayer#242

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>

CHANGELOG.md

@@ -7,6 +7,7 @@ Changelog
   * Icon background was changed to be consistent with other Nuvola apps.
   * SVG icons are optimized with scour to reduce their size.
   * A complete set of PNG icons with sizes 16, 22, 24, 32, 48, 64, 128 and 256 is built.
+  * Added information about contributing to the script.
 
 3.0 - May 23rd, 2016
 --------------------

CONTRIBUTING.md

@@ -0,0 +1,73 @@
+Contributing to Mixcloud script
+==================================
+
+:+1::tada: It seems you would like to contribute to the Mixcloud script for Nuvola Player.
+Great to have you here. Here are a few ways you can help make this script better! :tada::+1:
+
+Support & Bug Reporting
+-----------------------
+
+Whenever you encounter a bug in Nuvola Player, don't hesitate to report it. First of all, it is
+necessary to submit your issue to the right place.
+
+### Tiliado.eu Website
+
+If you have trouble with with **Tiliado.eu website** (tiliado.eu domain), your Tiliado account and
+memberships, contact [Tiliado support](mailto:support@tiliado.eu).
+
+### Tiliado Repositories
+
+If you have trouble with **Tiliado Repositories**, Tiliado Repository Installer and installation of
+Nuvola Player from Tiliado Repositories, report your issue at
+[Tiliado Repositories bug tracker](https://github.com/tiliado/tiliado-repositories/issues).
+
+### Nuvola Player and Streaming Services
+
+If you have any issue with the **Nuvola Player application** and supported streaming services,
+
+ 1. Check the
+    [List of Known Issues](https://github.com/tiliado/nuvolaplayer/wiki/Known-Issues) first.
+ 2. Take a brief look at
+    [Nuvola Player documentation](http://tiliado.github.io/nuvolaplayer/documentation/3.0.html)
+    as it might be helpful.
+ 3. Finally, follow 
+    [the Bug Reporting Guidelines](https://github.com/tiliado/nuvolaplayer/wiki/Bug-Reporting-Guidelines)
+    to create a new bug report.
+
+Development & Hacking
+---------------------
+
+If you would like to contribute some code to this repository, welcome aboard and read on! :+1:
+
+### Documentation
+
+  * See [Service Integration Development website](http://tiliado.github.io/nuvolaplayer/development/apps.html)
+  * or ask a question at [the nuvola-player-devel mailing list](https://groups.google.com/d/forum/nuvola-player-devel).
+
+### Developers without commit access to this repository
+
+  * Clone/fork the master branch via GitHub or `git clone`.
+  * Don't work on the master branch directly, but create a feature/topic/devel branch via
+    `git checkout -b branch-name`. Use meaningful branch name.
+  * Make your commits and follow
+    [guidelines for commit messages](http://tiliado.github.io/nuvolaplayer/development/apps/guidelines.html#commit-messages).
+  * Push your feature branch to GitHub.
+  * Create a pull request following
+    [guidelines for pull requests](http://tiliado.github.io/nuvolaplayer/development/apps/guidelines.html#pull-requests).
+
+### Developers with commit access to this repository
+
+  * Keep the `master` branch clean and functional, because it's the stable/production/release
+    branch.
+  * For one-commit changes without a need of code review, work directly on the master branch.
+    Follow
+    [guidelines for commit messages](http://tiliado.github.io/nuvolaplayer/development/apps/guidelines.html#commit-messages).
+  * For large changes, use feature/topic/devel branches. You can experiment and break things in
+    these branches, but they must be stable and functional when they are about to be merged back to
+    master. Follow
+    [guidelines for commit messages](http://tiliado.github.io/nuvolaplayer/development/apps/guidelines.html#commit-messages).
+  * Create a GitHub pull request following
+    [guidelines for pull requests](http://tiliado.github.io/nuvolaplayer/development/apps/guidelines.html#pull-requests)
+    if you would like to have a code review (preferred). Otherwise, feel free to perform a merge
+    on your own following
+    [guidelines for merge commits](http://tiliado.github.io/nuvolaplayer/development/apps/guidelines.html#merge-commits).