Change to `$HOME` in submodule example

_docs/037_bootstrap.md

@@ -43,6 +43,10 @@ initialize them after a successful clone.
 ```bash
 #!/bin/bash
 
+# Because Git submodule commands cannot operate without a work tree, they must
+# be run from within $HOME (assuming this is the root of your dotfiles)
+cd "$HOME"
+
 echo "Init submodules"
 yadm submodule update --recursive --init
 ```