Create `build:watch` command to simplify external contributions inside the core

[omariosouto]

Why?
People need to have an easy way to add new features and fix bugs

How?
Create a "build:watch": "" command that allows to work inside the examples folder with a live build and doing yarn link inside the respective folders.

I believe that we could use nodemon and use it's exec command to always run yarn unlink && yarn build && yarn link