Remove mint dev from Readme and replace with npm/yarn start

[nicofraisse]

What type of PR is this? (check all applicable)

• [ ] Refactor
• [ ] Feature
• [ ] Bug Fix
• [ ] Optimization
• [X] Documentation Update

Description

This PR removes everything related to mint dev from the documentation, and replaces it with npm start and yarn start.

Added to documentation?

• [X] readme
• [ ] no documentation needed

[nicofraisse]

Done 👍