Add page contents translation for the TOC

[yatil]

So that it is automatically translated in the future.

This PR prompted the issue: w3c/wai-intro-wcag#41

[shawna-slh]

Also "Summary".

This came up with translators earlier this month. I said something like: "Great idea -- although not a priority, so it might be a while until we get to it."

@yatil - I'm trying to limit extra work! ;-)

[yatil]

These are exactly the bugs and things I need to know about and at least log somewhere. :-)

[shawna-slh]

Well, I would not call them bugs. Enhancements.

+1 to log somewhere