README: Move info about programmatic APIKEY creation under API section
README: Move info about programmatic APIKEY creation under API section

The possibility for programmatic creation of APIKEY for Ampache or
Subsonic probably interests next to no-one. It was now moved away from
other Ampache/Subsonic information, to end of the document with other
API-related information.

Also some other tweaks were made on the document.

paulijar/music,paulijar/music,owncloud/music,owncloud/music,owncloud/music,paulijar/music,paulijar/music,paulijar/music,owncloud/music,owncloud/music