Add CRA note to caveats

[Timer]

What:

Note that Create React App does not suffer from a common problem using Macros.

Why:

facebook/create-react-app#2730 (comment)

We don't want users thinking they have to purge the cache, as this will be very detrimental to their rebuild speed.
It's also important because these configuration values are out of their reach; ejecting to "fix" this would be unnecessary.

[codecov]

Codecov Report

Merging #83 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master    #83   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           1      1           
  Lines          80     80           
  Branches       19     19           
=====================================
  Hits           80     80

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[kentcdodds]

Cool! Thanks. Maybe we could add documentation on what people can do in their own webpack/Babel config to avoid the problem for themselves.