make react-native-windows an optional peerDependency

[bell-steven]

While installing this, I get this warning

npm WARN @react-native-community/checkbox@0.5.9 requires a peer of react-native-windows@>=0.62 but none is installed. You must install peer dependencies yourself.

Peer dependencies are automatically installed on npm v7+, which is probably not what we want for non react-native-windows users.

References:
This twitter thread
NPM dependency docs

[nicholaslee119]

Thanks for your PR, It would be released in the next version

[bell-steven]

This may close #123

[pushpender-singh-ap]

@nicholaslee119 when do we get the next release?