Add link to devguide section on backporting in failure message

Author: StanFromIreland

miss_islington/tasks.py

@@ -198,7 +198,7 @@ async def backport_task_asyncio(
                 issue_number,
                 f"""\
                 Sorry, {util.get_participants(created_by, merged_by)}, I could not cleanly backport this to `{branch}` due to a conflict.
-                Please backport using [cherry_picker](https://pypi.org/project/cherry-picker/) on command line.
+                Please backport manually with the [cherry_picker](https://pypi.org/project/cherry-picker/) tool, see the [Backporting merged changes](https://devguide.python.org/getting-started/git-boot-camp/#backporting-merged-changes) section in the Python developer's guide for more information.
                 ```
                 cherry_picker {commit_hash} {branch}
                 ```
@@ -223,7 +223,7 @@ async def backport_task_asyncio(
                 f"""\
                 Sorry {util.get_participants(created_by, merged_by)}, I had trouble completing the backport.
                 Please retry by removing and re-adding the "needs backport to {branch}" label.
-                Please backport backport using [cherry_picker](https://pypi.org/project/cherry-picker/) on the command line.
+                If that does not work, please backport manually with the [cherry_picker](https://pypi.org/project/cherry-picker/) tool, see the [Backporting merged changes](https://devguide.python.org/getting-started/git-boot-camp/#backporting-merged-changes) section in the Python developer's guide for more information.
                 ```
                 cherry_picker {commit_hash} {branch}
                 ```