Update go get installation cmd to go install

[BrayFlex]

Fixes # README Installation with Go Fix: go get is not supported for external modules, go install is now the cmd

Checklist

• [ ] Added unit / integration tests for windows, macOS and Linux?
• [ ] Added a changelog entry in CHANGELOG.md?
• [X] Updated the documentation (README.md, docs)?
• [ ] Does your change work on Linux and Windows?
  • [X] Does your change work on macOS?

I believe the first 2 checklist items are not applicable and I am unable to test on Linux / Windows that go install github.com/commander-cli/commander/v2/cmd/commander@latest installs commander.