Add maintainance docs

Author: bbhtt

MAINT.md

@@ -0,0 +1,50 @@
+## Maintainance notes
+
+- Please see the [versioning policy](https://github.com/flatpak/flatpak-builder/tree/main?tab=readme-ov-file#supported-versions).
+- Stable branches will only get bugfixes and non-breaking enhancements.
+- Everything is merged to `main` and from time to time suitable changes
+  are backported to the stable `flatpak-builder-1.EVEN_MINOR.x`
+  branches. GitHub milestone can be used for tracking which PRs should
+  be backported.
+- Stable tags are created from `flatpak-builder-1.EVEN_MINOR.x` branch.
+- Unstable tags are created from the `main` branch.
+- The first release of a new stable release line eg. `1.6.0`
+  is tagged from `main`. After that the `flatpak-builder-1.6.x` branch
+  is to be created and the `1.6.1` is made from that branch. During this
+  time `main` should not receive breaking changes until the new
+  stable branch is created.
+
+## Releasing
+
+- Update the `NEWS`
+- Update version number in `meson.build` and `configure.ac`.
+- Open a  PR titled "Release $VERSION" with the above to see if CI passes.
+- Merge the PR to the target branch.
+- Check out the target branch, pull the above change locally and make
+  sure the submodules are correct and checked out.
+- Build with `meson` and `make`, with all options enabled.
+- Create a tarball with `make dist`. The tarball is created from a
+  clean checkout. It is produced as `flatpak-builder-$VERSION.tar.xz`.
+- Verify the project is buildable using the tarball. The tarball MUST
+  contain the submodule files.
+
+## Tagging
+
+- The tags are created in the `MAJOR.MINOR.PATCH` format eg. `1.4.6`
+  (WITHOUT the `v*` prefix).
+- Ideally the tags should be signed and annotated tags. Optionally
+  git-evtag can be used.
+- The tag message should have the changelog and the checksum of the
+  tarball that will be attached to GitHub releases.
+- Once the tag is pushed, a GitHub release from that tag is to be
+  created.
+
+  The release tag is the new tag, the title is `VERSION` and the release
+  body is the message from the tag. Additional notifications and details
+  can be documented to the release body.
+
+  Then the `flatpak-builder-$VERSION.tar.xz` tarball is to be attahced.
+  This is the primary way downstreams consume Flatpak builder.
+
+
+NOTE: GitHub releases are set as _immutable_, so please be careful.

README.md

@@ -73,3 +73,7 @@ Rarely used:
  * rpm2cpio & cpio
  * svn
  * bzr
+
+# Maintainance docs
+
+Please see the [maintainance docs](https://github.com/flatpak/flatpak-builder/blob/main/MAINT.md).