Fix Markdown in CONTRIBUTING file

I messed everything up trying to wrap lines, so ensure there are
newlines separating headers from paragraphs

CONTRIBUTING.md

@@ -1,8 +1,11 @@
 # Contributing to Facebook Open Source Projects
+
 We want to make contributing to Facebook Open Source Projects as easy and
 transparent as possible.
 
-## Pull Requests We actively welcome your pull requests.
+## Pull Requests
+
+We actively welcome your pull requests.
 
 1. Fork the repo and create your branch from `master`.
 2. If you've added code that should be tested, add tests.
@@ -11,20 +14,24 @@ transparent as possible.
 5. Make sure your code lints.
 6. If you haven't already, complete the Contributor License Agreement ("CLA").
 
-## Contributor License Agreement ("CLA") In order to accept your pull request,
-we need you to submit a CLA. You only need to do this once to work on any of
-Facebook's open source projects.
+## Contributor License Agreement ("CLA")
+
+In order to accept your pull request, we need you to submit a CLA. You only
+need to do this once to work on any of Facebook's open source projects.
 
 Complete your CLA here: <https://code.facebook.com/cla>
 
-## Issues We use GitHub issues to track public bugs. Please ensure your
-description is clear and has sufficient instructions to be able to reproduce
-the issue.
+## Issues
+
+We use GitHub issues to track public bugs. Please ensure your description is
+clear and has sufficient instructions to be able to reproduce the issue.
 
 Facebook has a [bounty program](https://www.facebook.com/whitehat/) for the
 safe disclosure of security bugs. In those cases, please go through the process
 outlined on that page and do not file a public issue.
 
-## License By contributing to Facebook Open Source Projects, you agree that
-your contributions will be licensed under the LICENSE file in the root
-directory of each project's source tree.
+## License
+
+By contributing to Facebook Open Source Projects, you agree that your
+contributions will be licensed under the LICENSE file in the root directory of
+each project's source tree.