Add some notes to the readme about queries that don't hit

We should mention something in the readme about the routine
process for deleting old queries and removing/rejecting
queries related to essentially incomplete bugs.

This has come up a few times in reviews so it's best to
document for expectations.

Change-Id: I2730f4947aa771704fb93fd824aac236d532527c
Merge "Add some notes to the readme about queries that don't hit"