Add Documentation to Examples for USGS's IV/DV Service

[heycatwonton]

Need to think about USGS'S IV service in the documentation - where does it make sense and what to add

• IV service is implemented in getting measurement timeseries tvp observations.
• Class is DataSynthesizer in synthesis.py in plugins
• In Documentation: DataSynthesizer is in KeyFunctions
• Might want to explain IV and DV service of the USGS plugin in documentation somewhere

Link back to basin3d-views get_timeseries_data call.

Documentation: https://basin3d.readthedocs.io/en/latest/

[heycatwonton]

@vchendrix @dschristianson what do you think about this?