📖 docs: (getting started ) add installation guide

[RayyanSeliya]

Summary

Adds the Installation guide to the getting-started section, covering three installation methods (installation script, Homebrew, and manual download), verification steps, and links to required tools.

Related issue(s)

Part of the documentation restructuring for the kflex.dev docsite development

[kubestellar-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[kubestellar-prow]

Hi @RayyanSeliya. Thanks for your PR.

I'm waiting for a kubestellar member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[clubanderson]

⚠️ Unit test failing due to stale base branch

This PR targets the doc-kubeflex branch which hasn't been updated since October 2025. Please merge main into doc-kubeflex or rebase onto main.

[clubanderson]

/ok-to-test

[kubestellar-prow]

@RayyanSeliya: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-kubestellar-kubeflex-test-unit	55e4696	link	true	/test pull-kubestellar-kubeflex-test-unit

Full PR test history

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository. I understand the commands that are listed here.