docs: netdev: document the existence of the mail bot

We had a good run, but after 4 weeks of use we heard someone
asking about pw-bot commands. Let's explain its existence
in the docs. It's not a complete documentation but hopefully
it's enough for the casual contributor. The project and scope
are in flux so the details would likely become out of date,
if we were to document more in depth.

Link: https://lore.kernel.org/all/[e-mail]/
Reviewed-by: Andrew Lunn <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

Documentation/process/maintainer-netdev.rst

···
 Updating patch status
 ~~~~~~~~~~~~~~~~~~~~~
 
-It may be tempting to help the maintainers and update the state of your
-own patches when you post a new version or spot a bug. Please **do not**
-do that.
-Interfering with the patch status on patchwork will only cause confusion. Leave
-it to the maintainer to figure out what is the most recent and current
-version that should be applied. If there is any doubt, the maintainer
-will reply and ask what should be done.
+Contributors and reviewers do not have the permissions to update patch
+state directly in patchwork. Patchwork doesn't expose much information
+about the history of the state of patches, therefore having multiple
+people update the state leads to confusion.
+
+Instead of delegating patchwork permissions netdev uses a simple mail
+bot which looks for special commands/lines within the emails sent to
+the mailing list. For example to mark a series as Changes Requested
+one needs to send the following line anywhere in the email thread::
+
+  pw-bot: changes-requested
+
+As a result the bot will set the entire series to Changes Requested.
+This may be useful when author discovers a bug in their own series
+and wants to prevent it from getting applied.
+
+The use of the bot is entirely optional, if in doubt ignore its existence
+completely. Maintainers will classify and update the state of the patches
+themselves. No email should ever be sent to the list with the main purpose
+of communicating with the bot, the bot commands should be seen as metadata.
+
+The use of the bot is restricted to authors of the patches (the ``From:``
+header on patch submission and command must match!), maintainers themselves
+and a handful of senior reviewers. Bot records its activity here:
+
+  https://patchwork.hopto.org/pw-bot.html
 
 Review timelines
 ~~~~~~~~~~~~~~~~