Fix typo in README.md (#540)

Summary:
Just fixed a small typo which was bothering me.

Pull Request resolved: #540

Reviewed By: ajinkya-ghonge, wenhaizhu, jinxinl22

Differential Revision: D57985038

Pulled By: chennyc

fbshipit-source-id: fc88a21a462d266ffe739ffe7293c57ec95be0c2

README.md

@@ -26,7 +26,7 @@ MPC applications typically need to access local data that is stored in the cloud
 ### Example: The Billionaire Game
 As an example of how you might use the PCF v2.0 APIs, we have included an example implementation of the classic [Billionaire](example/billionaire_problem/BillionaireProblemGame.h) game.  You can run the game in two terminals representing two players.  Each player will randomly return an integer from 0 to 1000000000 to represent the amount of money they have.  The game will compare the two integers and determine who is richer.
 
-Instructions on how to run the exmaple:
+Instructions on how to run the example:
 * Build the code and get the executable. Suppose the executable is `billionaire`.
 * Open one terminal and run `./billionaire`.
 * Open the other temianl and run `./billionaire --party=1 --server_ip=127.0.0.1`.