wqp.py documentation improvements

As noted by @jzemmels, a new dataretrieval-python user might find the swagger docs and webservice documentation a little tough to get the hang of. Ideally, we'd have the `kwargs` specified for each function within the function documentation, but it's tricky when the service arguments may not be stable over time. This increases developer burden to update documentation in the repository. However, there might be a compromise where we provide a little better descriptors of the functions and what the user might expect to learn from the webservice links/swagger docs.