Add docs/Guides submodule (mirror of WebKit wiki content)

[sideshowbarker]

* .gitmodules
* Makefile
* README.md
* docs/Guides

[stwrt]

Honestly, I really do not like this patch.

I ported over the wiki contents a while ago, and had not planned people to continue to add there. There appears to be a few new articles that popped up there recently that I was planning to copy over.

Having multiple places to write the documentation is quite inefficient, and the wiki is missing a lot.

[cdumez]

I ported over the wiki contents a while ago, and had not planned people to continue to add there. There appears to be a few new articles that popped up there recently that I was planning to copy over.

I intend to keep on using the wiki and keep the wiki up to date. Any content I maintain that gets copied over will very likely get outdated.