Making go-local-coauthors-plus a bit more ready for public consumption

- Added a README.md file
- Tweaked some conditionals so `coauthors_posts_links` doesn't fall over in a non GO environment.
- On new installs the cache option has autoload set to 'no'
	- Added a admin ajax endpoint to update existing installs
		- /wp-admin/admin-ajax.php?action=go_local_coauthors_plus_autoload_no
sure.