Twenty Seventeen: Deprecate GitHub source code

[jhabdas]

Please add some kind of source deprecation notice the GitHub repo. The current text slipped in at the top of the repo is woefully easy to miss. I've left an issue here to help highlight the need for this change and to help others with may have had the same misunderstanding:

​https://github.com/WordPress/twentyseventeen/issues/505

As an added bonus, it would be nice if you listed a way to CURL or download the latest source from the trunk for those who don't have time to figure all this out. Thank you.

[ocean90]

@karmatosed @obenland @davidakennedy Is this something you could handle please? Looks like we now have do the same for Twenty Sixteen.

[karmatosed]

Absolutely, I added messages to both repos and turned off issues, linking to trac as a way to report issues.

[jhabdas]

Thanks @karmatosed. For background, I opened this and the related issue because I dropped directly into a source file from GH search and began curling the file to a remote server I was using for prototyping while preparing for a WordCamp talk, causing me to begin curling outdated source code as the repos readme did not contain a notice of deprecation (my original ask).