Added firebse rule

Author: Sung Kim

firebase.rule.json

@@ -0,0 +1,23 @@
+{
+  "rules": {
+  "$roomname": {
+        "questions": {
+          ".read": true,  
+          ".write": true,
+          
+          // Must have echo, head, desc
+         // ".validate": "newData.hasChildren(['echo', 'head', 'desc', 'timestamp'])",
+
+          // a widget can have a title or color attribute
+          "echo": { ".validate": "newData.isNumber()" },
+          "head": { ".validate": "newData.isString()"},
+          "desc": { ".validate": true },
+          "timestamp": { ".validate": "newData.val() <= now" }  
+          
+          // but no other child paths are allowed
+          // in this case, $other means any key excluding "title" and "color"
+          //"$other": { ".validate": false }
+      }
+    }
+  }
+}