React-dropzone - warn consumers that major version has been updated

[nicolethoen]

Follow up to breaking change PR patternfly/patternfly-react#7926

This may not be something we can write a code mod for - some products might be relying (unadvisedly) on the PF react-dropzone dependency, so they'd need to make similar breaking changes in their project. We could print out a warning if they are using react-dropzone in their product at all?

Required actions:

1. Build codemod
2. Build test
3. Update readme with description & example