Contribution Policy added

CONTRIBUTING.md

@@ -0,0 +1,64 @@
+# How to contribute
+
+We encourage open source developers to support the Privacy Friendly Apps. 
+We also wish to keep it as easy as possible to contribute. There are a few 
+guidelines that we need contributors to follow.
+For further questions we refer to the contact details on the [Privacy Friendly Apps website](https://secuso.org/pfa). 
+
+## Reporting of Issues
+
+* Make sure you have a [GitHub account](https://github.com/signup/free).
+* Open an issue in the corresponding app's repository, assuming one does not already exist.
+  * Clearly describe the issue including steps to reproduce when it is a bug.
+    In some cases screenshots can be supportive. 
+  * Make sure you mention the Android version and the device you have used when 
+    you encountered the issue. 
+* Make your description as precise as possible.
+
+## Making Changes
+
+* Make sure you have a [GitHub account](https://github.com/signup/free).
+* Find an issue that you wish to close. If the issue you wish to close is not 
+  present, open it. Make sure that the issue has one of the following labels
+  which are set by our team:
+  * Bug
+  * Enhancement
+  * Help wanted
+  * No integration planned 
+  That means that we have already reviewed the issue. If you wish to add a 
+  translation, opening an issue is not required. 
+* Fork the repository on GitHub.
+* Create a topic branch from where you want to base your work (usually master branch).
+  * To quickly create a topic branch based on master, run `git checkout -b
+    fix/master/my_contribution master`. 
+  *	Please avoid working directly on the `master` branch.
+* Make commits of logical units in english language.
+* Make sure your commit messages are in the proper format. If the commit
+  addresses an issue filed in the Github repository, start the first line 
+  of the commit with a hash followed by the issue number (e.g. #42).
+* Make sure you have added the necessary tests for your changes.
+* Run all available tests to assure nothing else was accidentally broken.
+
+### Unwanted Changes
+
+The Privacy Friendly Apps are a group of Android apps that are optimized regarding
+the user's privacy. Therefore, Pull Requests that contain the following functionality
+will be rejected:
+* Analytics or advertisement frameworks
+* User tracking (e.g. sending of data to a third party)
+* Any that use of libraries that do not comply the license of the corresponding Privacy
+  Friendly App (GPLv3 or Apache2).  
+* Unnecessary use of Android permissions. If new functionality is added that requires
+  the usage of an Android permission you should clearly explain the Pull Request why
+  this permission is required.
+* New translations/languages  
+
+## Submitting Changes
+
+* Push your changes to a topic branch in your fork of the repository.
+* Submit a Pull Request to the repository of the corresponding Privacy Friendly App.
+* Indicate that you have read this policy by writing the second word of the section "unwanted changes"
+* Our team looks at Pull Requests on a regular basis and assigns a reviewer.  
+* After feedback has been given we expect responses within one month. After one
+  month we might close the pull request if no activity is shown.
+