FABJ-455 - update maintainers list

Proposal to add the following maintainers to fabric-sdk-java:

Andrew Coleman (currently also maintainer of fabric-sdk-node, fabric-gateway-java)
Mark Lewis (currently also maintainer of fabric-gateway-java)

Change-Id: I8985cca4c343cefd9d25e1905cf886398ee8a491
Signed-off-by: andrew-coleman <andrew_coleman@uk.ibm.com>

Author: andrew-coleman

MAINTAINERS.md

@@ -1,10 +1,12 @@
 ## Maintainers
 
 ### Active Maintainers
-| Name          | GitHub       | Gerrit       | email |
+| Name          | GitHub         | Gerrit         | email |
 |---|---|---|---|
-| Rick Rineholt | cr22rc        | rickr         | cr22rc@gmail.com       |
-| Gari Singh    | mastersingh24 | mastersingh24 | gari.r.singh@gmail.com |
+| Rick Rineholt | cr22rc         | rickr          | cr22rc@gmail.com          |
+| Gari Singh    | mastersingh24  | mastersingh24  | gari.r.singh@gmail.com    |
+| Andrew Coleman| andrew-coleman | andrew-coleman | andrew_coleman@uk.ibm.com |
+| Mark Lewis    | bestbeforetoday| bestbeforetoday| Mark.S.Lewis@outlook.com  |
 
 
 ### Retired Maintainers