fix env var escaping

Author: schworer

README.md

@@ -48,7 +48,7 @@ Install `httplib2` with `pip` or `easy_install`.
 
 
 
-**Note:** If you set the `**ZENCODER\_API\_KEY**` environment variable to your api key, you don't have to provide it when initializing Zencoder.
+**Note:** If you set the `ZENCODER_API_KEY` environment variable to your api key, you don't have to provide it when initializing Zencoder.
 
 ## Contributors
     Senko Rasic [github](http://github.com/senko)