Add footnote that abridge is included as submodule (#11)

* Add footnote that abridge is included as submodule

* Add command sequence to get started

- Move git submodule footnote inline

* Link to git submodule help

* The latest git-clone docs mention --recurse-submodules

Author: philderbeast

README.md

@@ -2,13 +2,20 @@
 
 ## Local installation
 
-The blog is made with [Zola], based on the [Abridge theme].
+The blog is made with [Zola] and based on the [Abridge theme] that is included
+as a Git [submodule][git-submodule].
 
 You will need:
   * The `zola` binary v0.19.1 or higher
 
 Run `zola serve` in order to serve the website and automatically render it when files change.
 
+```
+$ git clone [email protected]:haskell/blog.haskell.org.git --recurse-submodules
+$ cd blog.haskell.org
+$ zola serve
+```
+
 ## Contribute content
 
 ### Blog post structure
@@ -60,3 +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