Add documentation on how to validate changed records in a branch

[stepps00]

Non-validating records have recently made their way into the whosonfirst-data repository, causing distribution files to not include expected data. Add documentation and/or a script(s) that outline how to validate:

A. all changed records in a pull request/branch and
B. all records in a whosonfirst-data repository

See also:

• https://github.com/whosonfirst/go-whosonfirst-uri/
• https://github.com/whosonfirst/go-whosonfirst-validate
• https://github.com/whosonfirst/go-whosonfirst-validate#wof-validate-index (-mode files)