Link to git submodule help

Author: philderbeast

README.md

@@ -3,7 +3,7 @@
 ## Local installation
 
 The blog is made with [Zola] and based on the [Abridge theme] that is included
-as a git submodule.
+as a Git [submodule][git-submodule].
 
 You will need:
   * The `zola` binary v0.19.1 or higher
@@ -67,3 +67,4 @@ documentation-best-practices
 
 [Zola]: https://www.getzola.org/
 [Abridge theme]: https://abridge.pages.dev/overview-abridge/
+[git-submodule]: https://git-scm.com/docs/git-submodule