Update CONTRIBUTING.md

### Everyday commands

1. Build all packages:

* Build all packages:

    ```sh

    $ rush build

    ```

2. Watch changes and rebuild in all libraries:

* Watch changes and rebuild in all libraries:

    ```sh

    $ rush build:watch

    ```

3. Start demo dev-server:

* Start demo's dev-server:

    ```sh

    $ cd apps/demo

    $ npm run dev

    ```

Usually you need two terminals to run both 2 and 3.

Usually you need two terminals to run both 2 and 3 for testing your changes.

## FAQ