Update CONTRIBUTING.md (#3674)

Following my own experience getting set up to do Nuxt work recently, I've updated `CONTRIBUTING.md` in a way would have helped me greatly.

CONTRIBUTING.md

@@ -2,11 +2,45 @@
 
 1. [Fork](https://help.github.com/articles/fork-a-repo/) this repository to your own GitHub account and then [clone](https://help.github.com/articles/cloning-a-repository/) it to your local device.
 2. Run `npm install` to install the dependencies.
-3. Run `npm link` to link the local repository to NPM.
-4. Then npm links this repository inside any nuxt example app with `npm link nuxt`.
-5. Run `npm run build` or `npm run dev` inside your example app, if you created it with [nuxt starter template](https://github.com/nuxt-community/starter-template).
-6. Then you can run your example app with the local version of Nuxt.js (You may need to re-run the example app as you change server side code in the Nuxt.js repository).
 
-_Note that both npm and yarn have been seen to miss installing dependencies. To remedy that, you can either delete the node_modules folder in your example app and install again or do a local install of the missing dependencies._
+> _Note that both **npm** and **yarn** have been seen to miss installing dependencies. To remedy that, you can either delete the `node_modules` folder in your example app and install again or do a local install of the missing dependencies._
 
-Make sure to add tests into `test/` directory and try them with `npm test` before making a pull request.
+3. Add an example app to `examples/` before writing any code.
+4. Create a fixture app under `test/fixtures/`. See others for examples.
+
+To run an example or fixture app with your copy of Nuxt, do:
+
+```sh
+bin/nuxt examples/your-app
+bin/nuxt test/fixtures/your-fixture-app
+```
+
+> `npm link` could also (and does, to some extent) work for this, but it has been known to exhibit some issues. That is why we recommend calling `bin/nuxt` directly to run examples.
+
+Once you've modified Nuxt and seen your modifications reflected correctly in your example app and fixture, add `unit` and, if necessary, `e2e` tests that can ensure its functionality and future maintanability. Study other tests carefully for reference. 
+
+## Running specific tests
+
+```sh
+npm install jest -g
+jest test/unit/test.js
+```
+
+## Running test suites
+
+```sh
+yarn test
+```
+
+Or, per group:
+
+```sh
+yarn test:fixtures
+yarn test:unit
+yarn test:e2e
+```
+
+## Opening PRs
+
+- Please make sure your PR passes the lint test (`npm run lint`).
+- Please wait for tests to run and verify potential failures.

README.md

@@ -276,11 +276,6 @@ Thank you to all our [contributors](https://github.com/nuxt/nuxt.js/graphs/contr
 
 Please see our [CONTRIBUTING.md](./CONTRIBUTING.md)
 
-
-## Roadmap
-
-https://trello.com/b/lgy93IOl/nuxtjs-10
-
 ## License
 
 [MIT](https://github.com/nuxt/nuxt.js/blob/dev/LICENSE.md)