Authenticity of checksum file can not be assured

### How can we improve the documentation?

Writing this for the future me, as well as others it might help.

I was trying to install a newer version of golang, but was constantly failing with a "Authenticity of checksum file can not be assured" error. Looked online but only found references to a keyring nodejs script file that I don't have locally See [example issue](https://github.com/asdf-vm/asdf-nodejs/issues/174).

Turns out the solution was simply to update my plugin before installing a new version.

So

```
$ asdf plugin update golang
$ asdf install golang 1.25.0
```

This time, no issue any more "checksum verified".

I think that is asdf was telling me there was a newer version of the plugin somewhere, that'd be helpful.

Cheers!

Start by reviewing the documentation around `asdf plugin update` and `asdf install`, using the reported Golang installation commands as the example. Done should explain that updating the plugin can resolve checksum verification errors and make the suggested recovery steps easy to find.

Written by the indexing model from the issue text.