F citation cff

Adding a citation.cff file, see: https://citation-file-format.github.io/

RELEASE_GUIDELINES.md

@@ -24,6 +24,7 @@ guidelines of the CaosDB Project
    - `version` variables in `src/doc/conf.py`
    - Version on [setup.py](./setup.py): Check the `MAJOR`, `MINOR`, `MICRO`, `PRE` variables and set
      `ISRELEASED` to `True`. Use the possibility to issue pre-release versions for testing.
+   - `CITATION.cff` (update version and date)
 
 5. Merge the release branch into the main branch.