Update CONTRIBUTING.rst

CONTRIBUTING.rst

@@ -18,8 +18,6 @@ Making Changes
 
 -  Create a topic branch from where you want to base your work.
 -  This is usually the master branch.
--  Only target release branches if you are certain your fix must be on
-   that branch.
 -  To quickly create a topic branch based on master;
    ``git branch fix/master/my_contribution master`` then checkout
    the new branch with ``git checkout fix/master/my_contribution``.
@@ -40,6 +38,7 @@ Making Changes
 Submitting Changes
 ------------------
 
+-  Make sure there isn't already a Pull Request opened by somebody else.
 -  Push your changes to a topic branch in your fork of the repository.
 -  Submit a pull request to the repository.