Create MAINTAINERS.md

Create a MAINTAINERS file to align with OAI charter section 4.e.

>The maintainers of the TDC shall be those listed in the MAINTAINERS file in the project repository, available in the top level of the code repository.

AFAIK, this list represents the current people with access to push the green `Merge` button on the OpenAPI Spec repository

Author: RobDolinMS

MAINTAINERS.md

@@ -0,0 +1,7 @@
+* Darrel Miller [@darrelmiller](https://github.com/darrelmiller)
+* Jason Harmon [@jharmn](https://github.com/jharmn)
+* Jeremy Whitlock [@whitlockjc](https://github.com/whitlockjc)
+* Marsh Gardiner [@earth2marsh](https://github.com/earth2marsh)
+* Rob Dolin [@RobDolinMS](https://github.com/robdolinms)
+* Ron Ratovsky [@webron](https://github.com/webron)
+* Tony Tam [@fehguy](https://github.com/fehguy)