Add note about cloning this repo to README

README.md

@@ -1,3 +1,7 @@
 # Manski's DevLog
 
 For details on writing, see [README](content/__README.md) in the `content` directory.
+
+This repo contains submodules - so you need to clone it like this:
+
+    git clone --recurse-submodules https://github.com/skrysmanski/docs .