Add to search documentation how to get Virginia without West Virginia

[tucotuco]

Thus:

stateprovince:"Virginia" AND (NOT stateprovince:"West Virginia")

A query for

stateprovince:"Virginia" will return records for both states.

[tucotuco]

This could go on both the API search function page in this repository (https://github.com/VertNet/webapp/wiki/The-API-search-function) and on the Advanced Search documentation in the VertNet Resources. They should be separate issues, perhaps.

[pzermoglio]

I've added it to the API search function page, with examples, at the very end of:
https://github.com/VertNet/webapp/wiki/The-API-search-function#somequeryingexamples

[tucotuco]

Thanks to @pzermoglio. Back to @dbloom for incorporation in Portal Search document as well.