add document about maintainer addition

Author: eteq

policies/adding-new-maintainers.md

@@ -0,0 +1,23 @@
+This document describes the process for adding new people to maintainer roles.
+"Maintainer" here basically means any role with github write powers. The
+process is in the hands of the Coordination Committee according to
+[APE0](https://github.com/astropy/astropy-APEs/blob/main/APE0.rst), which also
+requires the comment period. The process is:
+
+1. Either the Coordination Committee or any community member including the 
+   nominee may nominate someone for a role via private or public email,
+   Slack message, in person request that is then recorded in meeting notes, etc.
+2. A Coordination Committee member then sends a message to the person
+   nominated, making sure they understand the role, its responsibilities, and
+   confirming that the nominee agrees. Suggested text of that message is 
+   [here](https://github.com/astropy/astropy-project/blob/main/messages/maintainer_access.md).
+3. If the nominee does not accept, the process stopps here.
+4. If the nominee does accept, a message goes out to the community, starting
+   a two-week clock on the feedback period [as required by APE0](https://github.com/astropy/astropy-APEs/blob/main/APE0.rst#responsibilities-and-authority).
+   The Coordination Committee member overseeing the process can make a PR at
+   this time adding the member to the roles page as a place for public comment.
+5. Once the two week period has elapsed, the coordination committee makes a
+   final decision based on any feedback. If the appointment is confirmed,
+6. The nominee is added to the roles page (i.e., the PR created in step 4 can
+   be merged), and the nominee receives the necessary Github or other 
+   permissions and a confirmation message to complete the process.