update README and package.json for development setup

[devvmh]

When following the README, I encountered two issues; this solves those issues.

1. Clarify need to create polis.config.js, and how to do it
2. Fix compilation error with react-tap-event-plugin per https://stackoverflow.com/questions/40670018

[devvmh]

Ah, I found #35

[patcon]

Thanks for opening a ticket @devvmh! We're planning to archive these old client repos soon, so hopefully it will be more clear for future travellers :)

cc: @metasoarous