Move content from W3C wiki to Github wiki, and close W3C wiki

[coolharsh55]

Community guidance and best practice (various sources) dictates information intended for development or long-form documentation of processes are better suited in a wiki. With this in mind, it would be prudent to provide helpful materials in the wiki e.g. contribution guidelines, rules and procedures, FAQ for adding new concepts.

My initial concern(s) about using Github wiki was regarding 1) platform lock-in - which is not valid as the wiki is itself a (separate) git repo which can be used/migrated to another platform; and 2) managing access control - which is also not valid as wiki access control is separate to the repo.