docs: add section about landing advisory update pull requests from the bot (#91)

I realized we didn't have any documentation for this, and the latest
regeneration has added a warning to an existing advisory - for now I've
kept this a bit light since we don't really have a clear sense of how
much actually work will be needed (and ideally it'll be very little),
but this should hopefully be enough to let others feel ok interacting
with the automated pull requests

Author: G-Rath

README.md

@@ -43,6 +43,23 @@ poetry run scripts/precache_nodes.py
 poetry run scripts/generate_osv_advisories.py
 ```
 
+### Landing automated advisory updates
+
+A
+[GitHub Actions workflow](https://github.com/ackama/drupal-advisory-database/blob/main/.github/workflows/generate.yml)
+runs regularly to regenerate the advisories, opening a pull request if there are
+changes.
+
+Before being landed the changes should be reviewed for accuracy especially with
+the version constraints and ranges - these will usually be flagged by the
+generation script as warnings included in the `database_specific` sections of
+the advisories where relevant.
+
+If an advisory does have a warning, you should aim to have it addressed using
+`patches.toml` described in the next section. This can be done by either pushing
+a new commit directly to the pull request branch, or through a new pull request
+after landing the changes to the advisories.
+
 ## Fixing incorrect data
 
 Sometimes an advisory will have incorrect data, such as an affected version