MESSy/CLaMS: Commit Changes to DKRZ server

see CONTRIBUTING.md in messy main directory

Before the very first commit configure the author name and email address to be used with your commits (saved in ~/.gitconfig):
```
git config --global user.name "firstname lastname"
git config --global user.email name@fz-juelich.de
```
Create issue on DKRZ server
- issue #xxx
- Description of issue: "CLaMS:..."
  (This makes it easy to search for all clams-specific changes)
Create corresponding branch xxx-description on DKRZ server
Update local repository
```
git pull
```
For further information see Update MESSy/CLaMS
Switch to new branch
```
git checkout xxx-description
```
=> already modified files are applied to the new branch
Check your changes and commit:
```
git status
git add [...]
git commit
```
Commit Message:
- first line with issue number
  - xxx: ...
  - (xxx: clams-submodul: ... -> all "clams" commits can be searched on DKRZ server!)
- empty second line
- additional explanatory text with as much details as desired from the third line onwards

Before pushing:

List all files to be pushed:

git diff --stat --cached origin/devel
git diff --stat --cached origin/xxx-description

View all differences in all files to be pushed:

git diff --cached origin/devel
git diff --cached origin/xxx-description