[issue35714] Document that the null character '\0' terminates a struct format spec

[Zackery Spytz]

Change by Zackery Spytz <zspytz at gmail.com>:


----------
pull_requests: +19678
pull_request: https://github.com/python/cpython/pull/20419

_______________________________________
Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue35714>
_______________________________________