Add cherry-picker documentation (apache#44118)

---------

Co-authored-by: GPK <gopidesupavan@gmail.com>

dev/README_AIRFLOW3_DEV.md

@@ -30,6 +30,8 @@
 - [Committers / PMCs](#committers--pmcs)
   - [Merging PRs for providers and Helm chart](#merging-prs-for-providers-and-helm-chart)
   - [Merging PR for Airflow 3 and 2.10.x / 2.11.x](#merging-pr-for-airflow-3-and-210x--211x)
+  - [How to backport PR with GitHub Actions](#how-to-backport-pr-with-github-actions)
+  - [How to backport PR with `cherry-picker` CLI](#how-to-backport-pr-with-cherry-picker-cli)
   - [Merging PRs 2.10.x](#merging-prs-210x)
   - [Merging PRs for Airflow 3](#merging-prs-for-airflow-3)
   - [Merging PRs for Airflow 2.11](#merging-prs-for-airflow-211)
@@ -122,6 +124,86 @@ Mistakes happen, and such backport PR work might fall through cracks. Therefore,
 
 This way release manager can verify (as usual) if all the "expected" PRs have been backported and cherry-pick remaining PRS.
 
+
+We are using `cherry-picker` - a [tool](https://github.com/python/cherry-picker) that has been developed by
+Python developers. It allows to easily cherry-pick PRs from one branch to another. It works both - via
+command line and via GitHub Actions interface.
+
+## How to backport PR with GitHub Actions
+
+When you want to backport commit via GitHub actions (you need to be a committer), you
+should use "Backport commit" action. You need to know the commit hash of the commit you want to backport.
+You can pin the workflow from the list of workflows for easy access to it.
+
+[!NOTE]
+It should be the commit hash of the commit in the `main` branch, not in the original PR - you can find it
+via `git log` or looking up main History.
+
+![Backport commit](images/backport_commit_action.png)
+
+Use `main` as source of the workflow and copy the commit hash and enter the target branch name
+(e.g. `v2-10-test`).
+
+The action should create a new PR with the cherry-picked commit and add a comment in the PR when it is
+successful (or when it fails). If automatic backporting fails because of conflicts, you have to revert to
+manual backporting using `cherry-picker` CLI.
+
+## How to backport PR with `cherry-picker` CLI
+
+Backporting via CLI might be more convenient for some users. Also it is necessary if you want to backport
+PR that has conflicts. It also allows to backport commit to multiple branches in the same command.
+
+To backport PRs to any branch (for example v2-10-test), you can use the following command:
+
+It's easiest to install it (and keep cherry-picker up-to-date) using `uv tool`:
+
+```bash
+uv tool install cherry-picker
+````
+
+And upgrade it with:
+
+```bash
+uv tool upgrade cherry-picker
+```
+
+Then, in order to backport a commit to a branch, you can use the following command:
+
+```bash
+cherry-picker COMMIT_SHA BRANCH_NAME1 [BRANCH_NAME2 ...]
+```
+
+This will create a new branch with the cherry-picked commit and open a PR against the target branch in
+your browser.
+
+If the GH_AUTH environment variable is set in your command line, the cherry-picker automatically creates a new pull request when there are no conflicts. To set GH_AUTH, use the token from your GitHub repository.
+
+To set GH_AUTH run this:
+
+```bash
+export GH_AUTH={token}
+Sometimes it might result with conflict. In such case, you should manually resolve the conflicts.
+Some IDEs like IntelliJ has a fantastic conflict resolution tool - just follow `Git -> Resolve conflicts`
+menu after you get the conflict. But you can also resolve the conflicts manually (git adds `<<<<<<<`, `=======` and
+`>>>>>>>` markers to the files with conflicts).
+
+```bash
+cherry_picker --status  # Should show if all conflicts are resolved
+cherry_picker --continue  # Should continue cherry-picking process
+```
+
+> [!WARNING]
+> Sometimes, when you stop cherry-picking process in the middle, you might end up with your repo in a bad
+> state and cherry-picker might print this message:
+>
+> > 🐍 🍒 ⛏
+> >
+> > You're not inside a cpython repo right now! 🙅
+>
+> You should then run `cherry-picker --abort` to clean up the mess and start over. If that does not work
+> you might need to run `git config --local --remove-section cherry-picker` to clean up the configuration
+> stored in `.git/config`.
+
 ## Merging PRs 2.10.x
 
 Make sure PR targets `v2-10-test` branch and merge it when ready.