Add <caption> elements to all documentation tables

[timwright12]

Describe the bug
Documentation tables on the baseline site don't have caption elements. It isn't required, but it would be nice to get them in there.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://baseline.10up.com/component/accordion/
2. Scroll down to a table
3. See error

Expected behavior
Captions should exist on table elements throughout the site.

[smy315]

I have some time today and will work on this.

[smy315]

PR: #236