doc: clarify adding ctx argument to check command in schema.py On IRC user was unsure what file was used for the 1.51 - 1.60 upgrade section: Enhancement to check command for Permissions added file name desription and example. Also marked it as optional. Clarified that if or when it becomes required there will be a new required upgrade direction.

#!/usr/bin/env python
from __future__ import print_function
import zlib, base64, sys
print(base64.encodestring(zlib.compress(sys.stdin.read())))