Document r263286.

Sponsored by:	The FreeBSD Foundation
Document r263212.

Sponsored by:	The FreeBSD Foundation
Document r263171.

Sponsored by:	The FreeBSD Foundation
Add reference to r263170.  The Radeon KMS driver was added in
r263170, and r263171 is the __FreeBSD_version bump.

Sponsored by:	The FreeBSD Foundation