[PATCH] zsh-development-guide: Document the new X-Seq autoreply bot.

[Daniel Shahaf <d.s@daniel.shahaf.name>]

---
Before anyone points it out, yes, we know the HTML archives aren't
updating yet.  We've haven't gotten around to setting mhonarc up.

 Etc/zsh-development-guide | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/Etc/zsh-development-guide b/Etc/zsh-development-guide
index cbada7de9..e8c292cfd 100644
--- a/Etc/zsh-development-guide
+++ b/Etc/zsh-development-guide
@@ -66,6 +66,14 @@ avoided further changes to our workflow.
    the mailing list sequence number. This number is generated by the list
    server and inserted as an X-Seq: header field in the e-mail.
 
+   Your email client may be able to be configured to show the X-Seq:
+   header by default, and probably has a way to view the raw full headers
+   of an email.  The X-Seq header is also shown on the
+   https://www.zsh.org/mla/ email archives.  We can also, upon request,
+   set up an email-based bot that, whenever you post a patch to the
+   mailing list, will send you an offlist reply with the X-Seq number of
+   your patch.
+
  * An entry in the ChangeLog file should be added manually before pushing
    a commit to the master repository. Don't create a separate change for
    this: amend the existing commit in your local repository.