DOC: Add short list-value example

Summary

Adds a short example of list-valued properties to the documentation

Focus

Check the new tutorial section for understandability.

Test Environment

make doc and look at the resulting html.

Check List for the Author

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• All automated tests pass
• [ ] Reference related Issues
• [ ] Up-to-date CHANGELOG.md
• Annotations in code (Gitlab comments)
  • Intent of new code
  • Problems with old code
  • Why this implementation?

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
• Check: Are there spezifications? Are they satisfied?

For further good practices have a look at our review guidelines.

src/caosdb/common/datatype.py

@@ -90,6 +90,7 @@ def is_reference(datatype):
     else:
         return True
 
+
 def get_referenced_recordtype(datatype):
     """Return the record type of the referenced datatype.
 
@@ -119,7 +120,8 @@ def get_referenced_recordtype(datatype):
             raise ValueError("list does not have a list datatype")
 
     if datatype == FILE:
-        raise ValueError("FILE references are not considered references with a record type")
+        raise ValueError(
+            "FILE references are not considered references with a record type")
 
     return datatype