docs: add getting started section to examples README

[VolodymyrBg]

This PR improves the documentation in the examples/README.md file by adding proper content to the "Getting started" section that was previously empty.

Changes

• Added instructions on how to run examples using Cargo
• Mentioned that each example has its own README with specific instructions
• Noted that most examples require multiple instances for P2P communication
• Listed prerequisites for running the examples

Motivation

New users looking to try out rust-libp2p examples would benefit from clear instructions on how to get started. The empty section could be confusing and might discourage them from exploring the examples. This change makes the documentation more user-friendly and reduces the barrier to entry for people wanting to learn about libp2p.

Related Issues

N/A

Testing

No testing required as this is a documentation-only change.

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• A changelog entry has been made in the appropriate crates

[elenaf9]

Thanks @VolodymyrBg!

[VolodymyrBg]

@elenaf9 Thanks, can it be merged, please?

[jxs]

I feel this is yet another airdrop farming PR, specially after the demanding to be merged.

[VolodymyrBg]

@jxs Hi, my pull request was approved what means it was useful as far as I understand. So I politely asked if the PR could be merged. I didn't demand to merge this PR. Sorry if something went wrong