Add CONTRIBUTING.md with setup instructions

Author: mattmazzola

CONTRIBUTING.md

@@ -0,0 +1,48 @@
+# Contributing
+
+## Setup
+
+Install Global Depenedencies if needed:
+```
+npm install -g typings gulp
+```
+
+Clone the repository:
+```
+git clone https://github.com/Microsoft/PowerBI-JavaScript.git powerbi-client
+```
+
+Install Dependencies:
+```
+npm install
+typings install
+``` 
+
+Build:
+```
+gulp build
+```
+Or if using VScode: `Ctrl + Shift + B`
+
+Test
+```
+// PhantomJS
+gulp test
+// Chrome (Singel Run: true)
+gulp test --debug
+// Chrome (Single Run: false)
+gulp test --debug --watch
+```
+
+The build and tests use webpack to compile all the source modules into one bundled module that can execute in the browser.
+
+## Known Problems:
+Currently the biggest problem is that `.d.ts` file is not automatically generated.
+The typescript compiler can output declaration files for each typescript file but does not yet have the capability to output a single declaratione file from multiple modules.
+
+See: https://github.com/Microsoft/TypeScript/issues/4433
+
+The current process is to run tsc with declarations then manually concatenate each file and remove the irrelavant import and export statements.
+If this becomes to much of a problem we could move all the source to a single file. 
+
+