Add information about updating the submodule and tagging commits

README.md

@@ -16,11 +16,27 @@ To build:
     make update html
 ```
 
-To build a binary Debian package:
+This should cause the `Librem_5` submodule to be updated if there are new commits
+in the [core user documentation repository](https://source.puri.sm/Librem5/librem5-user-docs-common).
+If the submodule has been updated, you will need to commit the change to the
+`Librem_5` directory.
+
+To build a binary Debian package for testing:
 ```
     debuild -b -us -uc
 ```
 
+This can be copied to the phone and installed using `dpkg`.
+
+## Updating the Debian package for the phone
+
+The `.gitlab-ci.yml` file will cause a new `deb` package to be built
+automatically. However, a signed tag is needed for the package to be built by
+the [Continuous Integration server](https://arm01.puri.sm/job/debs/).
+See the [Core Workflow](https://developer.puri.sm/Librem5/Apps/Packaging_Apps/Core_Workflow/index.html)
+section of the Librem 5 [developer documentation](https://developer.puri.sm/Librem5)
+for guidance.
+
 ## Copyright and License Information
 
 Copyright: Copyright (C) 2019 Purism SPC