Add explanation on how to write titles for this plugin to work

Author: thenikso

README.md

@@ -6,4 +6,6 @@ A Chrome Extension to add [SCRUM](https://en.wikipedia.org/wiki/Scrum_(software_
 
 ![Example screenshot](./screenshot.png)
 
-And that's it.
+You notes/PR/issues should have a title like `(2) My issue title` and the "(2)"
+will be converted in a nice tag. Also all projects lists will have the total count
+of story points in them next to the count of cards. That's it.