Link to Contribution Guidelines on README

[0xModene]

Is your feature request related to a problem? Please describe.
The README Contributing section should link to CONTRIBUTING.md

Describe the solution you'd like
Link to https://github.com/SetProtocol/index-ui/blob/master/CONTRIBUTING.md#-troubleshooting

[tytarman]

I'll take care of it. Was gonna ask if we should do that anyway.

[0xModene]

have at it