First pass on RFC process.

First pass on this document.

Bits that need updating:
* [ ] More on the description.
* [ ] Finish the template.
* [ ] Decide how RFC numbers are issued (see below).
* [ ] Determine the initial editor team.

On the topic of RFC numbers: do we want them at all? Its very convenient for compact discussions to have a short, unambiguous number so I am in favor, but the process would be a lot simpler without them (not having to update the filename and metadata after submission).

Another minor wart in the process here is that either immediately before or after merging an accepted proposal, the status field needs to be updated from Draft to Accepted.

Have at it! :)