Link to the canonical Launchpad PPA page

The previous URL (.../user/Packaging/PPA/) returns HTTP 200 but is a
client-side (JS/meta-refresh) redirect stub, so lychee's max_redirects=0 can't
see it. Point directly at the canonical page instead.

Part of STF-557.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: oschwald

README.dev.md

@@ -20,7 +20,8 @@ You may want to refer to the section about prerequisites.
 In order to upload a PPA, you have to create a launchpad.net account and
 register a GPG key with that account. You also need to be added to the MaxMind
 team. Ask in the dev channel for someone to add you. See
-https://documentation.ubuntu.com/launchpad/user/Packaging/PPA/ for more details.
+https://documentation.ubuntu.com/launchpad/user/reference/packaging/ppas/ppa/
+for more details.
 
 The PPA release script is at `dev-bin/ppa-release.sh`. Running it should guide
 you though the release, although it may require some changes to run on