[gimp-web] devel-docs: add a verification steps to the mirror procedure.

[Jehan <jehanp src gnome org>]

commit 236dd7c7a8b1dcf1bf7447c37973ae52ff4d544d
Author: Jehan <jehan girinstud io>
Date:   Tue Oct 5 21:50:05 2021 +0200

    devel-docs: add a verification steps to the mirror procedure.

 devel-docs/mirror-howto.md | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)
---
diff --git a/devel-docs/mirror-howto.md b/devel-docs/mirror-howto.md
index c2cff7fc..27278a4d 100644
--- a/devel-docs/mirror-howto.md
+++ b/devel-docs/mirror-howto.md
@@ -85,14 +85,20 @@ instance @Jehan can take care of part of the actions:
    other data. In "more", also add the report link.
    If other data needs to be updated, do so as well (for instance if
    other mirrors changed).
-11. Verify all mirrors (especially new ones) are well synced at least
+11. Run again:
+
+   ```sh
+   tools/downloads/update-mirrors.py --ssh-user <yourlogin>
+   ```
+   This time, it should tell you everything is fine.
+12. Verify all mirrors (especially new ones) are well synced at least
     for the last release:
     ```sh
     tools/downloads/gimp-check-mirrors.py
     ```
-12. Commit all the changes and push them to `gimp-web`'s `testing`
+13. Commit all the changes and push them to `gimp-web`'s `testing`
     branch.
-13. After a short time, make sure that testing's [sponsor 
page](https://testing.gimp.org/donating/sponsors.html)
+14. After a short time, make sure that testing's [sponsor 
page](https://testing.gimp.org/donating/sponsors.html)
     is properly updated.
 
 Of course, the public website will be updated when you merge `testing`