Added in guidelines for contributing to noVNC

In CONTRIBUTING.md, you can now find a set of guidelines for
contributing to the noVNC project.  They detail coding style
information, requirements for pull requests, and how to run
the unit tests.

CONTRIBUTING.md

+How to contribute to noVNC
+==========================
+
+We accept code via pull requests on GitHub.  There are several guidelines that
+we expect contributors submitting code requests to follow.  If you have issues
+following any of these guidelines, feel free to drop us a line by leaving a
+comment in the code request or sending us an email.
+
+Contributing Guidelines
+-----------------------
+
+* While we don't have an official coding style guide, please try to follow
+  the general coding style of the existing code.
+** Use four spaces instead of tabs 
+** prefix private variables and functions with an `_`
+
+* Please try to include unit tests for your code.  For instance, if you
+  introduce a new encoding, add a test to `tests/test.rfb.js` under the
+  "Encoding Handlers" section (basically, input a small pattern in your
+  encoding and make sure the pattern gets displayed correctly).  If you
+  fix a bug, try to add a unit test that would have caught that bug
+  (if possible -- some bugs, especially visual ones, are hard to test for).
+
+* Squash your commits down in to a clean commit history.  For instance, there
+  should not be "cleanup" commits where you fix issues in previous commits in
+  the same pull request.  Before you go to commit, use `git rebase -i` to
+  squash these changes into the relevant commits.  For instance, a good commit
+  history might look like "Added support for FOO encoding, Added support for
+  BAR message, Placed Button in UI to Trigger BAR" (where each comma denotes
+  a separate commit).
+
+* Add both a title and description to your commit, if possible.  Place more
+  detail on what you did in the description.
+
+Running the unit tests
+----------------------
+
+There are two ways to run the unit tests.  For both ways, you should first run
+`npm install` (not as root).
+
+The first way to run the tests is to run `npm test`.  This will run all the
+tests in the headless PhantomJS browser (which uses WebKit).
+
+The second way to run the tests is using the `tests/run_from_console.js` file.
+This way is a bit more flexible, and can provide more information about what
+went wrong.  To run all the tests, simply run `tests/run_from_console.js`.
+To run a specific test file, you can use the `-t path/to/test/file.js` option.
+If you wish to simply generate the HTML for the test, use the `-g` option, and
+the path to the temporary HTML file will be written to standard out.  To open
+this file in your default browser automatically, pass the `-o` option as well.
+More information can be found by passing the `--help` or `-h` option.
+
+
+Thanks, and happy coding!