docs(readme): add sample usage within a script (#54)

Author: quickjp2

README.md

@@ -28,3 +28,28 @@ Run `npm install`
 user1>> hubot user2 has jester role
 hubot>> OK, user2 has the jester role.
 ```
+
+## Sample Usage
+### Restricting commands
+```coffee
+module.exports = (robot) ->
+  # Command listener
+  robot.respond /some command/i, (msg) ->
+    role = 'some-role'
+    user = robot.brain.userForName(msg.message.user.name)
+    return msg.reply "#{name} does not exist" unless user?
+    unless robot.auth.hasRole(user, role)
+      msg.reply "Access Denied. You need role #{role} to perform this action."
+      return
+    # Some commandy stuff
+    msg.reply 'Command done!'
+```
+### Example Interaction
+```
+user2>> hubot some command
+hubot>> Access Denied. You need role some-role to perform this action.
+user1>> hubot user2 has some-role role
+hubot>> OK, user2 has the some-role role.
+user2>> hubot some command
+hubot>> Command done!
+```