MAINTAINERS: add Aleksa Sarai

Much of the work I've done in umoci is effectively rewriting parts of
image-tools so that they are better designed and stable. I feel very
strongly that most (if not all) of umoci should live within this
project.

As such, I feel that I'm sufficiently familiar with all of the many
implementation details necessary to correctly and sanely implement the
OCI image specification.

Signed-off-by: Aleksa Sarai <[email protected]>

Author: cyphar

MAINTAINERS

@@ -7,3 +7,4 @@ Stephen Day <[email protected]> (@stevvooe)
 Vincent Batts <[email protected]> (@vbatts)
 Xie Keyang <[email protected]> (@xiekeyang)
 Lei Jitang <[email protected]> (@coolljt0725)
+Aleksa Sarai <[email protected]> (@cyphar)