Template for message to astropy-dev for role changes (#341)

* Template for message to astropy-dev for role changes

* Apply suggestions from code review

* Update messages/role_annoucement.md

* Capitalization

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Co-authored-by: P. L. Lim <[email protected]>

Author: hamogu

messages/role_annoucement.md

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+Text for announcement to astropy-dev mailing list
+
+The CoCo proposes to [select as appropriate]
+- add/remove the following roles to the list of roles on the Astropy project:
+- add/remove the following people for role XXX in the Astropy project:
+
+See https://www.astropy.org/team for a list of current roles. Following APE 0 [1] we leave a two week long comment period for this proposal where you can comment publicly on the PR [2] or privately to the CoCo ([email protected] or DM one of them on Slack). If there are no objections after two weeks, the CoCo will merge the PR [3].
+
+Sincerely,
+Name
+(for the CoCo)
+
+[1] https://github.com/astropy/astropy-APEs/blob/main/APE0.rst
+[2] LINK TO PR HERE
+[3] Technically, APE0 only requires the two-week long comment period for additions, but following the same spirit, the CoCo also invites comments for removal unless the person in a role explicitly requested to be removed or did not respond to consecutive role surveys.