Merge branch 'master' of gitlab.mpcdf.mpg.de:vrs/gadget4

documentation/02_running.md

documentation/04_config-options.md

documentation/05_parameterfile.md

documentation/06_snapshotformat.md

documentation/07_diagnosticfiles.md

documentation/08_groupfiles.md

documentation/09_special_modules.md

documentation/10_examples.md

documentation/11_migration.md