Add missing word.

Author: octalmage

README.md

@@ -31,7 +31,7 @@ Install RobotJS using npm:
 ```
 npm install robotjs
 ```
-It's that easy! npm will download one of the prebuilt [binaries](https://github.com/octalmage/robotjs/releases/latest) your OS.
+It's that easy! npm will download one of the prebuilt [binaries](https://github.com/octalmage/robotjs/releases/latest) for your OS.
 
 You can get npm [here](https://nodejs.org/en/download/) if you don't have it installed.