Updated cintribution guidelines

CONTRIBUTING.md

 # GIT Workflow
 
-Follow the ideas of [a-successful-git-branching-model](http://nvie.com/posts/a-successful-git-branching-model),
-especially
+Follow the git workflow:
 - Create a new branch for all new features, following the naming convention
   `feature/XYZ`
-- Merge features in the `develop` branch only
 - Correct Bugs in issue branches, following the naming convention `issue/XYZ`
-- Merge issues in the `develop` branch, except when it is a hotfix, then merge
-  to `master` and `develop`
-- For all merges create a meaningful *Merge Request* in GitLab
+- For features and issues *Merge Request* into the master branch should be created in GitLab
+- Do not push into `master` directly
+- Releases are created in a new branch `release/VERSION` that is not deleted after merged into master.
+  After the merge, a tag with name `vVERSION` should be created.
 
 # Code Style-Guide
 
@@ -44,24 +43,6 @@ files, such as `math.h` (remember that windows files-systems are case insensitiv
 thus, there is no difference between `math.h` and `Math.H`.)
 
 ## Generale file structure
-Every header file should start with a copyright notice and an include guard `#pragma once`,
-where the text of the copyright notice is given in the file `tools/license.templ.txt`
-and can automatically by added, using the script files in the `tools` directory:
-
-``` c++
-// Software License for AMDiS
-//
-// Copyright (c) 2015 Institute for Scientific Computing, Technische Universitaet Dresden
-// All rights reserved.
-// Authors: Simon Praetorius
-//
-// This file is part of the AMDiS Library
-// see also the LICENSE file in the distribution.
-
-#pragma once
-```
-
-After the include guard a list of include files can be added, see *Names and Order of Includes*.
 
 ### Names and Order of Includes
 
@@ -84,9 +65,7 @@ For example, the includes in `io/VtkWriter.cpp` might look like this:
 #include "io/VtkWriter.hpp"
 
 // [open]mpi header
-#ifdef HAVE_PARALLEL_DOMAIN_AMDIS
 #include <mpi.h>
-#endif
 
 // std c++ headers
 #include <cmath>
@@ -141,7 +120,7 @@ double const& d_ref = d;
 
 ### Functions
 Try to put all parameters in the line of the function declaration until it exceeds
-the maximum line length. Then list remaining arguments aligned with the first 
+the maximum line length. Then list remaining arguments aligned with the first
 function argument.  Follow the style of the brackets, like
 
 ```c++
@@ -166,7 +145,7 @@ public:
     : member1_(arg1)
     , member2_(arg2)
   {}
-  
+
 private:
   Arg1 member1_;
   Arg2 member2_;