[RFR] Remove bad advice about npm link

[fzaninotto]

Using npm link creates two versions or React, and causes the dreadful error:

Uncaught Invariant Violation: addComponentAsRefTo(...): Only a ReactOwner can have refs. You might be adding a ref to a component that was not created inside a component's render method, or you have multiple copies of React loaded (details: https://fb.me/react-refs-must-have-owner).

[fzaninotto]

Closes #26

[nonotest]

Hello,
If someone does need to link against a local version, you can bypass the addComponentAsRefTo error like this:

# link the component
cd my-app
npm link ../my-react-component

# link its copy of React back to the app's React
cd ../my-react-component
npm link ../my-app/node_modules/react

source: http://stackoverflow.com/questions/31169760/how-to-avoid-react-loading-twice-with-webpack-when-developing

I think it might be useful to re-add that bit in the doc.

[fzaninotto]

I think it's out of the admin-on-rest scope, so we won't add it back to the doc. But thanks for the pointer!