docs: Document examples

[SapiensAnatis]

Document the process for running the examples. This was fairly non-obvious and I spent a fair bit of time trying and failing to get a client credentials token to work before finding in some discussion that this is known not to work.

The wiki mentions using the oauth example as a way to get a token and I think that is likely to be the best way to get a token for the purposes of running the examples too.

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I was able to get all of the examples except one to work using the method described, although for play_connect this is irrelevant since it acquires its own token via OAuth. The one I wasn't able to get to work was get_token which seems to be broken as per #1532, however this does work if you make the suggested fix to use login5().

[Copilot]

Pull Request Overview

This PR adds comprehensive documentation for running examples in the librespot library, addressing a gap in user guidance. The documentation clarifies the token acquisition process and provides step-by-step instructions for running examples.

• Adds a new README.md file in the examples directory with detailed usage instructions
• Documents the OAuth-based token acquisition process as the recommended approach
• Provides concrete examples of how to run the examples with proper arguments

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