Add usage instructions.

README.md

@@ -1,3 +1,7 @@
 # Wallabag Install Script
 
 I was annoyed with the clunky install instructions / two seperate pages for Wallabag. I wrote a script to automate that process.
+
+# Usage
+
+`curl -s https://git.coolaj86.com/josh/wallabag-install/raw/branch/master/install.sh | bash`