Add info about gwlevels service

[ehinman]

Added a couple of sentences about the change to the gwlevels service in an attempt to catch/inform users that they need to update their version to leverage the new service.

[thodson-usgs]

data obtained from WQP legacy profiles will not include new USGS data or recent updates to existing data.

Is the information in the README correct? In separate conversations, I've been told the legacy profiles DO and DO NOT return new USGS data.

[thodson-usgs]

Fine to occasionally use the README in this manner, but the principal source for this type of information should be the release notes. I would include your note there: https://github.com/DOI-USGS/dataretrieval-python/releases/v1.0.10

[ehinman]

@thodson-usgs the legacy profiles do not include updated/new USGS discrete samples, but they DO include updated/new discrete samples from EPA/STORET.

Also, we recently received an inquiry about the gwlevels service returning an error when using dataretrieval-python, and it was because they didn't realize that the services had been updated and that their version of dataretrieval was using the decommissioned service. This is the root of the update to the README. I'm not sure everyone knows to check the release notes, though we could make that big and bold at the top of the readme.

[lstanish-usgs]

@ehinman the new warnings look good to me! I agree with @thodson-usgs that the updates to GWL should be in the auto-generated release notes, ideally we could modify those as needed so that they can be interpreted by users in a meaningful way.

[thodson-usgs]

I'm not sure everyone knows to check the release notes, though we could make that big and bold at the top of the readme.

That's fine, and yes, many users don't, but you should always assume this to be the case and be wary of any package that doesn't.

ideally we could modify those as needed so that they can be interpreted by users in a meaningful way.

Yes, you can edit them by clicking on the release (link above). I typically start with the auto-generated notes, then rewrite or expand as needed.

[ehinman]

Anything else I need to do for this PR? I think it's ready to merge. @thodson-usgs @lstanish-usgs

[thodson-usgs]

looks good. thanks, @ehinman

[lstanish-usgs]

@ehinman looks good! Merge away