Merge pull request 'feature/extends_readme' (#10) from...

Merge pull request 'feature/extends_readme' (#10) from peters/VirtualFluids_dev:feature/extends_readme into develop

CONTRIBUTING.md

-Contributing
-============
+# Contributing
+
 If you want to contribute to VirtualFluids, your help is very welcome.
 To contribute use a pull request as follows:
 
@@ -23,3 +23,19 @@ To contribute use a pull request as follows:
 your extra branch(es).
 
 And last but not least: Always write your commit messages in the present tense. Your commit message should describe what the commit, when applied, does to the code – not what you did to the code.
+
+## Documentation
+
+To build sustainable research software, it is mandatory to document code. 
+Even if it turns out that some developments are not continued, documentation is important to help future scientists to learn from the own experiences.  
+
+The documentation of the source code takes place…
+
+- in commit messages  
+  - As it is possible to put all the information into the commit messages, we want to keep the messages short and on a higher level of abstraction.
+  - The commit message should briefly summarize what the commit does to the code. 
+
+- in source code
+  - VirtualFluids is using Doxygen to generate Documentation from within the source code
+   - In most of the cases comment should describe ***why*** something was implemented and not ***how***.
+   - if available add formulars, references to scripts, paper, and all information you got linked to the implemented code