Instructions out of date for RHEL 8/9

When I try to install Ruby on RHEL (8/9) with ASDF, then yum and dnf note that there is no longer a package called `libyaml-devel`.

In recent versions of RHEL, the package is hidden by default. RHEL users will need to explicitly enable some package groups:

```
# RHEL 8 based distros:
dnf config-manager --set-enabled powertools

# RHEL 9 based distros:
dnf config-manager --set-enabled crb

dnf install libyaml-devel
```

Per https://github.com/rvm/rvm/issues/5288#issuecomment-1387705721

For comparison, RVM uses Ruby's built-in libyaml implementation:

https://github.com/rvm/rvm/issues/2998#issuecomment-330061538

Also, the GCC version is out of date.

This issue appears to be specific to the underlying rbenv/ruby-build system:

https://github.com/rbenv/ruby-build/issues/2437