Update contributing.md

Author: ujjwalkarn

contributing.md

@@ -1,13 +1,14 @@
-If you want to contribute to this list (please do), send me a pull request.
+If you want to contribute to this list (please do), send me a pull request. Since we want this list to be useful in the long, **please submit only high quality links**.
 
 ## Adding to this list
 
 Please ensure your pull request adheres to the following guidelines:
 
 - Please search previous suggestions before making a new one, as yours may be a duplicate.
+- Make sure your link has a useful and relevant title.
 - Please make an individual pull request for each suggestion.
 - Please use [title-casing](http://titlecapitalization.com) (AP style). 
-- Please use the following format: `[List Name](link)`
+- Please use the following format: `[Useful Title](link)`
 - Link additions should be added to the bottom of the relevant category.
 - New categories or improvements to the existing categorization are welcome.
 - Please Check your spelling and grammar.