Add basic imagine doc.

Signed-off-by: crynobone <crynobone@gmail.com>
Update 2.1 changelog.

Signed-off-by: crynobone <crynobone@gmail.com>
Merge branch '2.1' into 2.2
Update 2.2 changelog.

Signed-off-by: crynobone <crynobone@gmail.com>