Update README.md

Author: joelgrus

README.md

@@ -21,7 +21,8 @@ python recommender_systems.py
 
 Additionally, I've collected all the [links](https://github.com/joelgrus/data-science-from-scratch/blob/master/links.md) from the book.
 
-And, by popular demand, here's an [index of functions](https://docs.google.com/spreadsheets/d/1mjGp94ehfxWOEaAFJsPiHqIeOioPH1vN1PdOE6v1az8/edit?usp=sharing) defined in the book, by chapter and page number. (Right now it's just a spreadsheet, I'm working on making it easier to use.
+And, by popular demand, I made an index of functions defined in the book, by chapter and page number. 
+The data is in a [spreadsheet](https://docs.google.com/spreadsheets/d/1mjGp94ehfxWOEaAFJsPiHqIeOioPH1vN1PdOE6v1az8/edit?usp=sharing), or I also made a toy (experimental) [searchable webapp](http://joelgrus.com/experiments/function-index/).
 
 ## Table of Contents