Readme - Reorganize and improve installation instructions.

[MAXimized490]

Very open to opinions about these changes. This is just what I felt made more sense to me after running through the installation.

Brief Summary of Changes

• Mostly moved text around without making content changes.
• Rewrite prerequisites section.
• Modified npm install step to be paste-able into CLI.
• More explanation around creating .env file.
  • Moved all sections about environment variables here.
  • Included warning about confusing etc/passwd and /etc/passwd. I had to reread this a few times thinking I was crazy, but maybe just me.
• Provide path for ZT1 auth token.
• Moved summary of listening states to a new reference section.