Automate steps 3-5 in readme of installation.

[aniketpanjwani]

Steps to reproduce the problem:

Installation is a slight pain, and it shouldn't be that hard to make it easier.

Any other comments? What have you tried so far?

1. In make init, add a pipenv shell line at the end.
2. Figure out how to automatically add certificates from ~/.mitmproxy to Chrome/Firefox's respective certificate authorities, and add those lines in make init.
3. Add the following two lines in make init:

• sudo sysctl -w net.ipv4.ip_forward=1
• sudo sysctl -w net.ipv6.conf.all_forwarding=1
  The only hard part is figuring out how to automate the certificate authorities.