feat(renovatebot): add page about running post-upgrade tasks

Documents changes done in https://gitlab.developers.cam.ac.uk/uis/devops/infra/gitlab-bots-deployment/-/merge_requests/156

docs/howtos/renovatebot/post-upgrade-tasks.md

@@ -15,6 +15,8 @@ configuration option) in order to be executed.
 [Our configuration](https://gitlab.developers.cam.ac.uk/uis/devops/infra/gitlab-bots-deployment/-/blob/main/renovatebot-config.js?ref_type=heads#L97)
 is set up such that it can call scripts in the `./.renovate/` directory in the root that start with `post-upgrade*`.
 
+Note: make sure that the script is executable.
+
 Examples usages:
 
 {% raw %}
@@ -45,5 +47,3 @@ Or:
 ```
 
 {% endraw %}
-
-Note: make sure that the script is executable.