Update CONTRIBUTING.md

Makes it more clear regarding the URL to the fork.

Fix #58

Author: sikachu

CONTRIBUTING.md

@@ -74,7 +74,10 @@ git push origin my-feature-branch
 
 #### Make a Pull Request
 
-Go to https://github.com/contributor/activerecord-session_store and select your feature branch. Click the 'Pull Request' button and fill out the form. Pull requests are usually reviewed within a few days.
+Go to your fork at
+`https://github.com/[your github username]/activerecord-session_store` and
+select your feature branch. Click the 'Pull Request' button and fill out the
+form. Pull requests are usually reviewed within a few days.
 
 #### Rebase