Document GamaClass

TODO in astroquery/astroquery/gama/core.py (15)
```
class GAMAClass(BaseQuery):
"""
TODO: document
"""

request_url = 'http://www.gama-survey.org/dr3/query/'
timeout = 60
```

Start by reading the GAMAClass definition in astroquery/astroquery/gama/core.py and nearby GAMA query code to determine what the class provides. Document the class where the TODO appears, including only behavior supported by the surrounding implementation, then run the relevant project documentation or test checks if available.

Written by the indexing model from the issue text.