Add Steam API

Include Steam API in video games section.

README.md

@@ -72,6 +72,7 @@ A collective list of JSON APIs for use in web development.
 | Pokéapi | The RESTful Pokémon API | No |[Go!](http://pokeapi.co) |
 | Giant Bomb | Video Games | No |[Go!](http://www.giantbomb.com/api/documentation) |
 | Comic Vine | Comics | No | [Go!](http://comicvine.gamespot.com/api/documentation) |
+| Steam | Steam Client API | Yes | [Go!] (https://developer.valvesoftware.com/wiki/Steam_Web_API) |
 
 ### Media