Update the RELEASING notes
kms: add public API to override the default configuration of outputs

Add API to allow complex applications using the KMS backend
to go almost straight to direct configuration (which is not possible
because Cogl needs to be in charge of buffers and FB objects).

https://bugzilla.gnome.org/show_bug.cgi?id=705837

Reviewed-by: Robert Bragg <robert@linux.intel.com>