Correct table documentation in Remarkup reference

Summary: Ref T10570. Earlier work on that task made tables activate even if indented so they work in quoted blocks. However, the documentation doesn't explicitly mark them in code blocks, so it turned them into markup.

Test Plan:
Used bin/diviner generate to regenerate documentation, verified it now renders properly.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10570

Differential Revision: https://secure.phabricator.com/D15619