Improve examples rendering in docs and GitHub

[hmellor]

• Renames the md files to README.md so that they are rendered when browsing GitHub
• Adds some README.md files to multi-file examples which had no md, and therefore were missing from the docs

[github-actions]

👋 Hi! Thank you for contributing to the vLLM project.

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To run CI, PR reviewers can either: Add ready label to the PR or enable auto-merge.

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[DarkLight1337]

Thanks for fixing!

[DarkLight1337]

Hmm the build is failing