Include detailed backporting process to the doc (#4499)

doc/contribute/release_ccf.rst

@@ -10,7 +10,7 @@ Patching a release, ie. issuing a ``N.0.x+1`` version when the current version i
     1. Apply commits to ``release/N.0.x``, and/or cherry-pick them from ``main``
     2. Tag head of ``release/N.x`` as ``ccf-N.0.x+1``
 
-.. tip:: Alternatively, pull requests merged to ``main`` with the ``auto-backport`` and ``N.x-todo`` GitHub label(s) will be automatically backported to the corresponding LTS branch(es).
+.. tip:: Alternatively, pull requests merged to ``main`` with the ``auto-backport`` and ``N.x-todo`` GitHub label(s) will be automatically backported to the corresponding LTS branch(es). See `Labelling LTS PRs`_ section for more details. 
 
 Create an LTS release
 ---------------------
@@ -30,10 +30,10 @@ Labelling LTS PRs
 
 To keep track of which changes should be merged to LTS branches and then confirm them before cutting LTS releases, the following policy should be used:
 
-    1. A PR targetting ``main`` which contains changes that should also reach the N.x LTS should be labelled in GitHub with ``N.x-todo``
+    1. A PR targetting ``main`` which contains changes that should also reach the N.x LTS should be labelled in GitHub with ``N.x-todo`` and ``auto-backport``. ``auto-backport`` label will trigger a github action to backport automatically.  
     2. Where possible ``N.x-todo`` PRs should contain the minimal set of changes with no dependencies on earlier PRs, so they can be more easily cherry-picked
     3. A PR targetting an LTS branch (``release/N.x``) should be labelled in Github with ``N.x-backport``, so it can be easily found with a filter
     4. A PR targetting an LTS branch which is constructed primarily of a cherry-pick from ``main`` should be named consistently as ``Cherry-pick #<PR_ID> to N.x LTS``, so it can be easily correlated with the corresponding ``N.x-todo`` PR. If an LTS PR contains commits from multiple PRs to ``main``, each should be mentioned in the PR title, eg ``Port <foo> to N.x LTS (#PR1_ID, #PR2_ID, ...)```
-    5. Once a corresponding cherry-pick has been merged to the LTS branch, the ``N.x-todo`` label can be removed from the original PR
+    5. If the backport happened via the ``auto-backport`` github action, ``backported`` label will be automatically added to the ticket. Otherwise, you will need to manually add ``backported`` label once it's merged. 
 
 Before creating an LTS release, the releaser should do a scan of PRs and ensure that there are none with ``N.x-todo`` label. If any exist, they should be merged to the LTS branch before releasing, and those candidate labels removed.