fix: add Makefile local setup commands

[pratik-naik003]

Description of Changes

This PR adds a root Makefile with simple local development commands for the website:

• make setup to initialize the Docsy submodule and install Node dependencies
• make serve to start the local Hugo server
• make build to build the site

It also updates the README local setup instructions to use these make commands instead of the longer manual sequence.

This improves the contributor experience and makes the local setup flow easier to follow.

Related Issues

Closes: #4453

Checklist

• You have signed off your commits
• Ensure you follow best practices from our contributing guide.
• (for big changes) I will post screenshots of the changes in a PR comment

[google-oss-prow]

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[google-oss-prow]

Hi @pratik-naik003. Thanks for your PR.

I'm waiting for a kubeflow 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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[Arhell]

/ok-to-test

[pratik-naik003]

/assign @pratik-naik003