updated mongo notes for 'distinct'

mongo.md

@@ -28,6 +28,8 @@
 
 ` db.<collection_name>.findOne({<key-value pair condition>}) ` show the first object in collection; condition is optional
 
+` db.<collection_name>.distinct('<property_name>) ` list all the distinct values present for given property
+
 ` db.<collection_name>.update() ` update the object. 
 - `.update({<mathcing_condition>}, {<updated_value>}, {upsert: true/false}) ` If the upsert value is true then the new object is created if there is no object with given matching condition otherwise ignores
   - ` <update_value> ` If the object is given directly, then it will override the content of previous object