Update contribute_container.md

contribute_container.md

-# Contributing using Docker Containers
+# Contributing Using Local Docker Container
 
 ## Prerequisites
 
 Assuming you have:
 * A system with running Docker installation
 * All necessary access/execution rights
-* A gitlab clone
+
+## Fork an Clone Repository
+All contributing starts with forking the repository to either [gitlab.hrz.tu-chemnitz.de](https://gitlab.hrz.tu-chemnitz.de) or any other git service, e.g., [gitlab.com](https://www.gitlab.com), [github.com](https://www.github.com) or your personal preference. Now, create a local clone of your fork with one of these two ways:
+ ```Shell Session 
+ ~ git clone git@gitlab.hrz.tu-chemnitz.de:LOGIN/hpc-compendium.git 
+ 
+ ~ git clone https://gitlab.hrz.tu-chemnitz.de/LOGIN/hpc-compendium.git 
+ ```
 
 ## Start the Docker Containers