Add contributing notes

Author: reinink

.github/CONTRIBUTING.md

@@ -0,0 +1,85 @@
+# Contributing
+
+Thanks for your interest in contributing to Tailwind CSS! Please take a moment to review this document **before submitting a pull request**.
+
+## Pull requests
+
+**Please ask first before starting work on any significant new features.**
+
+It's never a fun experience to have your pull request declined after investing a lot of time and effort into a new feature. To avoid this from happening, we request that contributors create [an issue](https://github.com/tailwindcss/tailwindcss/issues) to first discuss any significant new features. This includes things like adding new utilities, creating new at-rules, or adding new component examples to the documentation.
+
+## Coding standards
+
+Our code formatting rules are defined in [.eslintrc](https://github.com/tailwindcss/tailwindcss/blob/master/.eslintrc). You can check your code against these standards by running:
+
+```sh
+npm run style
+```
+
+To automatically fix any style violations in your code, you can run:
+
+```sh
+npm run style --fix
+```
+
+## Running tests
+
+You can run the test suite using the following commands:
+
+```sh
+npm test
+```
+
+Please ensure that the tests are passing when submitting a pull request. If you're adding new features to Tailwind, please include tests.
+
+## Building the documentation
+
+Tailwind uses the [Jigsaw](http://jigsaw.tighten.co/) static site generator for its documentation. Here is how you can generate the documentation locally:
+
+1. Go to your Tailwind folder
+
+    ```sh
+    cd tailwindcss
+    ```
+
+2. Install JS dependencies
+
+    ```sh
+    npm install
+    ```
+
+3. Transpile the source code
+
+    ```sh
+    npm run prepare
+    ```
+
+4. Go to docs folder
+
+    ```sh
+    cd docs
+    ```
+
+5. Install PHP dependencies for docs (requires Composer: https://getcomposer.org)
+
+    ```sh
+    composer install
+    ```
+
+6. Install JS dependencies for docs
+
+    ```sh
+    npm install
+    ```
+
+7. Run the build to generate the static site
+
+    ```sh
+    npm run dev
+    ```
+
+8. View the static site at `/tailwind/docs/build_local`, or you can run the Jigsaw server:
+
+    ```sh
+    ./vendor/bin/jigsaw serve
+    ```

README.md

@@ -7,3 +7,7 @@ A utility-first CSS framework for rapidly building custom user interfaces.
 ## Documentation
 
 For full documentation, visit: https://tailwindcss.com/
+
+## Contributing
+
+If you are interested in contributing to Tailwind, please take a moment to read our [contributing docs](https://github.com/tailwindcss/tailwindcss/blob/master/.github/CONTRIBUTING.md) **before submitting a pull request**.