Update README with badges, sample index and links

[Ahmedatef5O5]

Replace this paragraph with a description of what this PR is changing or adding, and why. Consider including before/after screenshots.

List which issues are fixed by this PR. For larger changes, raising an issue first helps reduce redundant work.

Pre-launch Checklist

• [ ] I read the Flutter Style Guide recently, and have followed its advice.
• [ ] I signed the CLA.
• [ ] I read the Contributors Guide.
• [ ] I have added sample code updates to the changelog.
• [ ] I updated/added relevant documentation (doc comments with ///).

If you need help, consider asking for advice on the #hackers-devrel channel on Discord.

[google-cla[bot]]

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View this failed invocation of the CLA check for more information.

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[ericwindmill]

In addition to signing the CLA, please write a description of what the PR is changing and why