Dead link in main README

**Describe the bug**
In the main READMe of the project a link with text "How to play with the POC" in the section "How to play with the POC" 

**To Reproduce**
Steps to reproduce the behavior:
1. Go to README
2. Click on 'How to play with the POC'
4. See error in your browser

**Expected behavior**
The link would refers to page docs/ropsten.md.


