Update READMEs

[toshan-luktuke]

This PR aims to add consistency in READMEs and instructions in VisualCircuit. A short summary of changes is as follows:

• Updates the port used by backend to connect to the frontend from 3000 to 4000. As 4000 was the port being used in the frontend, previous iterations required this to be updated manually by the user.
• Separates the instructions to start VC+ into its own separate README in VC+/ in order to make the normal process of starting normal VisualCircuit simpler.
• Changes the port number in the backend README to 8080, as that is the current port being used for the backend.