Better document how to add new loaders after ejecting

[gaearon]

The existing comment is too easy to miss.

See http://stackoverflow.com/questions/41042479/create-react-app-with-sass-not-loading-styles.

We need to make it more obvious.

[ro-savage]

@gaearon - I have submitted PR #1499 to make the comment stand out more.

I have made the original comment stand out more with some spacing, and given a more practical example and have added a new comment to the end of the loaders array where a person would usually add a new loader to warn them to update the exclude list.

[ro-savage]

New PR #1500 to fix noob mistakes and to get a nice round PR number.

[Timer]

Resolved by #1500.