README.md is stale, need to document current libkrun requirements for developers

[nirs]

The readme is correct for latest release (v1.1.1) using libkrun-efi.dylib.

• Current code is using the generic libkrun (libkrun.1.dylib) and requires installing the firmware manually.
• The [building from source][src] section is broken now if you build from main.
• Building with locally built libkrun (e.g. in /usr/local) is not documented, but needed for testing changes in libkrun

Suggested solution:

• Keep user level installation instructions in REEADM.md
• Move development docs to docs/development.md
  • document building with latest libkrun release (/opt/homebrew)
  • document building with upstream libkrun (/usr/local)
  • document manual firmware install

[nirs]

#93 documents now default (/usr/local) and Homebrew build (/opt/homebrew).

[nirs]

#98 updated the tap dependency. The firmware is still not installed in the make install or documented.