add Contributing.md first pass

Author: etpinard

CONTRIBUTING.md

@@ -1 +1,69 @@
-yolos!
+# Contributing to plotly.js
+
+### Opening issues
+
+Search for existing and closed issues. If your problem or idea is not addressed
+yet, [please open a new issue](https://github.com/plotly/plotly.js/issues/new).
+
+### Development
+
+**Prerequisites**:
+
+- git
+- [node.js](https://nodejs.org/en/). We recommend using node.js 4.2.1 (LTS).
+  Upgrading and managing node versions can be easily done using
+  [`nvm`](https://github.com/creationix/nvm) or its Windows alternatives.
+
+**Step 1** Clone the plotly.js repo and install its dependencies
+
+```
+git clone https://github.com/plotly/plotly.js.git
+cd plotly.js
+npm install
+```
+
+**Step 2** Build plotly.js
+
+```
+npm run build
+```
+
+The build script combines:
+
+- `npm run preprocess`, which converts `scss` and `svg` assets to `js` and
+- `npm run bundle`, which runs
+  [browserify](https://github.com/substack/node-browserify) on the source files
+
+**Step 3** Start test dashboard
+
+```
+npm run start-test_dashboard
+```
+
+This command bundles up the source files with source maps, starts
+[watchify](https://github.com/substack/watchify) file watcher (making the your
+dev plotly.js bundle update every time a source file is saved) and opens up
+a tab in your browser.
+
+### Testing
+
+```
+npm test
+```
+
+Jasmine tests are run in a browser using
+[karma](https://github.com/karma-runner/karma)
+
+```
+npm run test-jasmine
+```
+
+Image pixel comparison tests are run in a docker container
+
+```
+npm run test-image
+```
+
+### Repo organization
+
+### Coding style