Add component for meta-information

This includes stuff that is not directly API documentation, but supportive of it, such as:

* XML registry / JSON profile schema documentation
* Vulkan Style Guide (and equivalents in other components, if they exist)
* Proposal template
* etc. (this list to be expanded)

There is pushback to putting this type of material in with the actual API documentation, such as #67.

Needs input from other component owners as to what belongs in this category.