doc: Improve docker example to mount in $HOME for easy config access

I'm surprised no one has asked any questions about this.

Author: nhooyr

doc/install.md

@@ -174,7 +174,11 @@ code-server
 # It will also mount your current directory into the container as `/home/coder/project`
 # and forward your UID/GID so that all file system operations occur as your user outside
 # the container.
+#
+# Your $HOME is mounted at $HOME within the container to ensure you can easily access
+# your code-server config in ~/.config/code-server/config.json
 docker run -it -p 127.0.0.1:8080:8080 \
+  -v "$HOME:/home/coder" \
   -v "$PWD:/home/coder/project" \
   -u "$(id -u):$(id -g)" \
   codercom/code-server:latest