adds contributing guidelines

Author: Nick Salloum

CONTRIBUTING.md

@@ -0,0 +1,30 @@
+# Contributing
+
+We love pull requests from everyone, and this is the place to go in order to publish one of those pull requests :)
+
+* Fork, then clone the repo:
+
+  ```
+  git clone [email protected]:your-username/flexgrid.css.git
+  ```
+
+* Install dependencies:
+
+  ```
+  npm install
+  ```
+
+* Work only in the `src/flexgrid.scss` file, and develop using gulp:
+
+  ```
+  gulp watch // => watches flexgrid.scss for changes and compiles to dist
+  gulp       // => compiles to dist
+  ```
+
+* Push to your fork and [submit a pull request](https://github.com/axiomzen/flexgrid.css/compare/).
+
+At this point you're waiting on us. We like to at least comment on pull requests within three business days (and, typically, one business day). We may suggest some changes or improvements or alternatives.
+
+Some things that will increase the chance that your pull request is accepted:
+
+* Add [examples](https://github.com/axiomzen/flexgrid.css/tree/master/examples). Use the [index.html](https://github.com/axiomzen/flexgrid.css/blob/master/examples/index.html) file as a base.