Improve wording in CONTRIBUTING.md

This fixes microsoft#2

Author: Immo Landwerth

CONTRIBUTING.md

@@ -21,9 +21,10 @@ let everybody know that you want to work on it.
    is none, create one.
 2. Create a fork in GitHub
 3. Create a branch off the `master` branch. Name it something that that makes
-   sense, such as `issue-123`.
+   sense, such as `issue-123`. This makes it easy for you to figure out what
+   the branch is used for.
 4. Commit your changes and push your changes to GitHub
-5. Create a pull request against our `master` branch
+5. Create a pull request against the origin's `master` branch
 
 ## DOs and DON'Ts