Move editorial process into repo README

[rmbaxter67]

The repo README isn't particularly useful at the moment.

The working group's editorial policy is a Google doc.

Proposal: transfer the contents of the Google doc into the README and retire the Google doc. Continue management of the editorial process doc under GitHub.

Cf. also #11

[rmbaxter67]

Actually, combining info from the ed process doc and the charter doc into a new working practices README is probably a better approach.