[doc] update repository docs

borrowing some of @notplant's wording in the README:
 https://git.coopcloud.tech/coop-cloud/mumble/pulls/1/files

MAINTENANCE and PULL_REQUEST_TEMPLATE are copied from traefik as per
 https://docs.coopcloud.tech/maintainers/maintain/#templates
with modifications to allow for single maintainers

MAINTENANCE.md

@@ -0,0 +1,31 @@
+# Traefik Recipe Maintenance
+
+All contributions should be made via a pull request. This is to ensure a
+certain quality and consistency, that others can rely on.
+
+## Maintainer Responsibilities
+
+A recipe maintainer has the following responsibilities:
+
+- Respond to pull requests / issues within a week
+- Make image security updates within a day
+- Make image patch / minor updates within a week
+- Make image major updates within a month
+
+In order to fullfill these responsibilities a recipe maintainer:
+
+- Has to watch the repository (to get notifications)
+- Needs to make sure renovate is configured properly
+
+## Pull Requests
+
+A pull request can be merged if it is approved by at least one maintainer. Even though it is okay to merge a pull request with one approval, it is always better if all maintainers looked at the pull request and approved it.
+
+Pull requests opened by a maintainer need to be approved by another maintainer. If there is only one maintainer, reviews from operators are recommended but not required.
+
+## Become a maintainer
+
+Everyone can apply to be a recipe maintainer:
+1. Watch the repository to always get updates
+2. Add your self to the list in the [README.md](./README.md) and open a new pull request with the change.
+3. Once the pull request gets merged you will be added to the [mumble maintainers team](https://git.coopcloud.tech/org/coop-cloud/teams/mumble-maintainers).