;doc: RELEASING.md: start capturing some org notes here

RELEASING.md

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+# Releasing
+
+Guidance for release managers and maintainers.
+
+Terminology:
+
+- "main" = the master branch, might get renamed in future.
+- "release" = a release branch, such as 1.22.
+
+## Changelogs
+
+Always maintain changelogs in main.
+
+Apply [CONTRIBUTING.md#commit-messages](CONTRIBUTING.html#commit-messages) rules
+when commiting, pushing, or reviewing/merging pull requests. 
+`tools/commitlint` helps with this, run locally and in CI.
+
+Use `./Shake changelogs` to update them from recent commit messages.
+
+## Minor release
+
+Checklist:
+
+- create release branch if none\
+  `git branch RELEASEBRANCH RELEASETAG`\
+  `git branch 1.22-branch 1.22`
+- update main changelogs\
+  - `./Shake changelogs`
+  - do at least basic editing - drop things, move things
+  - `./Shake changelogs -c`
+- review changes so far, estimate which packages will be released
+- add "unreleased" minor release heading in main changelogs, immediately above previous release heading
+  ```
+  # LATESTHASH
+
+  ...CHANGES...
+  
+  # X.Y.1 unreleased  <- new heading
+
+  # X.Y YYYY-MM-DD
+  ```
+- cherry pick changes to release
+  1. always update main changelogs first
+  2. cherry pick commits
+  3. move corresponding change items under minor release heading in main changelogs
+- finalise release
+  - add date to minor release heading in main changelogs
+  - copy the minor release section from main changelogs to release changelogs