Updated command line for syncing fork w/ main repo

via:
https://help.github.com/articles/configuring-a-remote-for-a-fork/

CONTRIBUTING.md

@@ -54,7 +54,7 @@ Notes:
 ## Keep sync with original repo
 First time, add a remote with the upstream
 ```
-git remote add upstream git@github.com:yclas/yclas.git
+git remote add upstream https://github.com/koseven/koseven.git
 ```
 
 Everytime you want to sync just