Checkout Polymer using bower instead of the raw repository.

third_party/polymer/platform/CONTRIBUTING.md

+# Contributing
+
+Want to contribute to Polymer? Great!
+
+We are more than happy to accept external contributions to the project in the form of [feedback](https://groups.google.com/forum/?fromgroups=#!forum/polymer-dev), [bug reports](../../issues), and pull requests.
+
+## Contributor License Agreement
+
+Before we can accept patches, there's a quick web form you need to fill out.
+
+- If you're contributing as an individual (e.g. you own the intellectual property), fill out [this form](http://code.google.com/legal/individual-cla-v1.0.html).
+- If you're contributing under a company, fill out [this form](http://code.google.com/legal/corporate-cla-v1.0.html) instead.
+
+This CLA asserts that contributions are owned by you and that we can license all work under our [license](LICENSE).
+
+Other projects require a similar agreement: jQuery, Firefox, Apache, Node, and many more.
+
+[More about CLAs](https://www.google.com/search?q=Contributor%20License%20Agreement)
+
+## Initial setup
+
+Here's an easy guide that should get you up and running:
+
+1. Setup Grunt: `sudo npm install -g grunt-cli`
+1. Fork the project on github and pull down your copy.
+   > replace the {{ username }} with your username and {{ repository }} with the repository name
+
+        git clone git@github.com:{{ username }}/{{ repository }}.git --recursive
+
+    Note the `--recursive`. This is necessary for submodules to initialize properly. If you don't do a recursive clone, you'll have to init them manually:
+
+        git submodule init
+        git submodule update
+
+    Download and run the `pull-all.sh` script to install the sibling dependencies.
+
+        git clone git://github.com/Polymer/tools.git && tools/bin/pull-all.sh
+
+1. Test your change
+   > in the repo you've made changes to, run the tests:
+
+        cd $REPO
+        npm install
+        grunt test
+
+1. Commit your code and make a pull request.
+
+That's it for the one time setup. Now you're ready to make a change.
+
+## Submitting a pull request
+
+We iterate fast! To avoid potential merge conflicts, it's a good idea to pull from the main project before making a change and submitting a pull request. The easiest way to do this is setup a remote called `upstream` and do a pull before working on a change:
+
+    git remote add upstream git://github.com/Polymer/{{ repository }}.git
+
+Then before making a change, do a pull from the upstream `master` branch:
+
+    git pull upstream master
+
+To make life easier, add a "pull upstream" alias in your `.gitconfig`:
+
+    [alias]
+      pu = !"git fetch origin -v; git fetch upstream -v; git merge upstream/master"
+
+That will pull in changes from your forked repo, the main (upstream) repo, and merge the two. Then it's just a matter of running `git pu` before a change and pushing to your repo:
+
+    git checkout master
+    git pu
+    # make change
+    git commit -a -m 'Awesome things.'
+    git push
+
+Lastly, don't forget to submit the pull request.