Documentation: Promote Python 3 syntax for bytes

The documentation use python 2 syntax to describe bytes as `str`. This is very misleading.

Do you want a PR to replace `'foo'` with `b'foo'` everywhere?

Start by locating the FoundationDB documentation examples that describe Python byte strings; the issue does not name specific files or tests. Review each occurrence of Python 2-style string literals used as bytes and define done as consistently using Python 3 byte literals without changing unrelated examples.

Written by the indexing model from the issue text.