Downloading a PR and Reviewing it. (Path-Check#82)

Added info on how to download a PR from a Forked Repo in order to review it.

.github/CONTRIBUTING.md

@@ -60,6 +60,34 @@ code releases.
 * A team member will review the pull request, request change or approve and
   merge into the `develop` branch.
 
+## Reviewing Pull Requests
+
+* Open the PR on Github. At the top of the PR page is a number which identifies it -123 and the name of the author's branch -branch-name. Copy down both of these.
+
+* Open git bash and ensure your working directory is clean by running ```git status```
+
+* Get a copy of the PR by typing ```git fetch upstream pull/<id>/head:<new local branch>```. In this example you would type git fetch upstream pull/123/head:branch-name
+
+* Now that you have a copy of the branch, switch to it using ```git checkout branch-name```. Your directory will now be an exact copy of the PR. Be sure to tell the author about any bugs or suggestions, as you cannot add your own changes to a pull request directly.
+
+* When you are done checking out their work, use ```git checkout master``` to return to your local version 
+
+### Git Aliases to help with pull request reviews 
+
+Aliases are shortcuts that you can define in git bash (or linux/mac) that reduces typing and minimizes errors. The following commands create two aliases, one for grabbing a PR and switching to that branch. The other one deletes the branch.
+
+Copy/paste each line (one at a time) to gitbash or terminal window.
+
+```git config --global --add alias.pr '!f() { git fetch -fu ${2:-upstream} refs/pull/$1/head:pr/$1 && git checkout pr/$1; }; f'```
+
+and
+
+```git config --global --add alias.pr-clean '!git checkout master ; git for-each-ref refs/heads/pr/* --format="%(refname)" | while read ref ; do branch=${ref#refs/heads/} ; git branch -D $branch ; done'```
+
+Once created the aliases are used as shown below.
+* To pull a pull request: ```git pr <id>``` to use the example above git pr 123
+* To delete all the pull requests created locally: ```git pr-clean```
+
 # Additional Resources
 
 * [General GitHub documentation](http://help.github.com/)