Clarify RHEL 9 support

[evanstoner]

The docs claim a requirement of RHEL >= 8.7. When running on RHEL 9:

[estoner@rhel9arm microshift-demos]$ ./scripts/configure-builder
Error: RHEL version must be >= 8.7 (have: 9.1).

The version check is performed piecemeal, major then minor: https://github.com/redhat-et/microshift-demos/blob/main/scripts/configure-builder#L19-L21

When I remove this version check, a package cannot be found:

[estoner@rhel9arm microshift-demos]$ ./scripts/configure-builder
# Installing experimental 'ostree' version (with support for embedding containers)
[sudo] password for estoner: 
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   389  100   389    0     0   2197      0 --:--:-- --:--:-- --:--:--  2197
# Installing ImageBuilder tools
Updating Subscription Management repositories.
Copr repo for ostreerhel8 owned by walters                                                            20 kB/s | 3.3 kB     00:00    
Package bash-completion-1:2.11-4.el9.noarch is already installed.
Package podman-2:4.2.0-7.el9_1.aarch64 is already installed.
No match for argument: syslinux
Package jq-1.6-12.el9.aarch64 is already installed.
Package wget-1.21.1-7.el9.aarch64 is already installed.
Error: Unable to find a match: syslinux

Is RHEL 9 supported, or is the requirement actually RHEL >= 8.7 and < 9.0?

Version: hello-microshift-v0.0.1-9-gc04f62e

[dhellmann]

MicroShift 4.12 is supported on RHEL 8 versions 8.7 and later. RHEL 9 support will come with a future version.