docs: mention packages in HACKING.md

docs/HACKING.md

@@ -23,6 +23,21 @@ test executable. For features at a higher level, tests in `src/test/` are very
 strongly recommended. If that is not possible, integration tests in `test/` are
 encouraged. Please always test your work before submitting a PR.
 
+## Installing packages built from the main branch
+
+Packages for main distributions are built on the SUSE Open Build Service and
+repositories are published, so that they can be installed and upgraded easily.
+
+Instructions on how to add the repository for each supported distribution can
+[be found on OBS.](https://software.opensuse.org//download.html?project=system%3Asystemd&package=systemd)
+The `systemd-boot` file is signed for Secure Boot, the self-signed certificate
+can be downloaded for enrollment. For example, when using MOK Manager:
+
+```sh
+$ wget https://build.opensuse.org/projects/system:systemd/signing_keys/download?kind=ssl -O- | openssl x509 -inform pem -outform der -out obs.der
+$ run0 mokutil --import obs.der
+```
+
 ## Hacking on systemd with mkosi
 
 [mkosi](https://mkosi.systemd.io/) is our swiss army knife for hacking on