internal/gophers: add missing documentation
internal/gophers: add missing documentation

This is a step towards improving the usability of this package.

Use myself as an example of the types of queries that GetPerson
accepts.

Updates golang/go#27631

Change-Id: I3f4d497eb237958c652e51e03fd2459f0f9df8ef
Reviewed-on: https://go-review.googlesource.com/c/build/+/195064
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/build,golang/build,golang/build,golang/build