updated README with Ref docs

README.md

@@ -151,4 +151,21 @@ ddb = SimpleTable('maintable',PrimaryKey={'Name':'_id','Type':'String'})
 
 ### Ref
 
-This class represents a reference to 
+This class represents a reference
+
+```python
+import sammy as sm
+
+
+sam = sm.SAM(Description='A hello world application.',render_type='yaml')
+
+sam.add_parameter(sm.Parameter(name='Bucket',Type='String'))
+
+sam.add_parameter(sm.Parameter(name='CodeZipKey',Type='String'))
+
+sam.add_resource(
+    sm.Function(name='HelloWorldFunction',
+        Handler='sample.handler', Runtime='python3.6', CodeUri=sm.S3URI(
+            Bucket=sm.Ref(Ref='Bucket'),Key=sm.Ref(Ref='CodeZipKey'))))
+
+```