expand contributing instructions

Author: milancurcic

README.md

@@ -10,3 +10,8 @@ submit a PR that adds a subdirectory with the following format:
 ```
 <event-name>-<topic>
 ```
+
+and in that directory add a README.md that contains your name, title, and 
+abstract.
+Any other files in the directory will be your presentation assets--slides, web 
+pages, videos, etc.