Feature Request: a command to add an existing version to goenv (instead of installing it)

[hmijail]

Jenv has an option to add an already-installed Java version to its list of known installed versions.
That would also be useful in goenv, and would allow us to bypass issue #106.

[ChronosMasterOfAllTime]

@hmijail the issue is that certain architectures are not supported in older releases of go, and would require to be built from source.

That being said, this is "fixed" with a current workaround to display an architecture isnt supported. Automation is currently grabbing new versions of golang for us, so we dont need to rely on users creating PRs