Created Contributing (markdown)

Contributing.md

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+If you're not familiar with pdf.js first see the readme getting started section.
+
+## Contributing Code
+An overview how to contribute code to the pdf.js project.  The basic workflow:
+
+1. fork
+1. feature branch
+1. make changes
+1. run lint and testing
+1. push changes to your fork/branch
+1. create pull request
+1. code review & automated testing
+1. merge into the master
+
+### The Bare Necessities
+* git client
+* git hub account
+* python
+* make
+* jslint
+
+If you're familiar with github and doing feature branches you can skip down to "4) Run Lint and Testing"...
+
+### 1) Fork
+To fork the repository you'll need to sign up for a github account. Once you have an account just click the little fork button up top. Now that you have your fork you'll need to clone it (replace `<YOUR USERNAME>`):
+```
+git clone git://github.com/<YOUR USERNAME>/pdf.js.git
+```
+### 2) Branch
+We try to do everything in feature branches. For example, to create and switch to a type 3 font branch use:
+```
+git checkout -b type3fontsupport
+```
+### 3) Changes
+Now that you have you're branch you can edit/add/delete files.  You'll then want to stage and locally commit your changes.  I won't go into this since there are lots of guides that explain git.
+
+### 4) Run Lint and Testing
+**Run Lint**
+
+Make sure your code follows our style guides, run from the pdf.js folder:
+```
+make lint
+```
+**Run Testing**
+
+To ensure your changes didn't introduce any regressions you'll need to run the testing framework. There are three basic types of tests:
+
+* load - just checks if the pdf file can be loaded without crashing
+* eq - a reference test which takes correctly rendered snapshots and compares them to the snapshots created by the current code
+* fbf - a forward back forward test
+
+The reference tests require you to generate the original snapshots for comparison.  The snapshots should be generated before you make any changes to the code.  To generate these snapshots:
+
+```
+cd pdf.js/test/
+python test.py -m --browserManifestFile=resources/browser_manifests/browser_manifest.json
+```
+That will create the references files in pdf.js/test/tmp so you'll then need to rename "tmp" to "ref" or move it to your branch and rename. Now to run the tests from the pdf.js folder:
+```
+make test
+```
+
+### 5) Push Changes
+After lint and all tests pass, push changes to your fork/branch on github.
+
+### 6) Pull Request
+Create a pull request on github for your feature branch.  The code will then be reviewed and tested further by our pdfbot.
+
+### 7) Code Review & Further Testing
+A collaborator will kick off further testing and do a code review.
+
+### 8) Merging to Master
+If all goes well a collaborator will merge all your changes into the main repo.