Context

The module docstring for cursor.py reads "Cursor class to iterate over Mongo query results" and the class AsyncCursor has no class-level docstring at all reads "Create a new cursor." Neither makes it clear that this cursor is specifically returned by collection.find() and is distinct from CommandCursor/AsyncCommandCursor, which is returned by commands like aggregate, listIndexes, and listCollections.

A reader encountering AsyncCursor for the first time has no way to know from the docstring alone why two cursor classes exist or when they would encounter each one.

This is a lower-cost alternative to PYTHON-5899 (renaming to FindCursor) that improves discoverability without a public API change.

Definition of done

• Add Update class-level docstring to AsyncCursor / Cursor that explains it is returned by collection.find() and distinguishes it from CommandCursor
• Update the module docstring in cursor.py to reflect the same
• Update _RawBatchCursor / _RawBatchCursor docstrings similarly if applicable

Pitfalls

None — purely additive documentation change.