docs: update README to reflect change from snippets to samples for cl…

[adriennetacke]

…arity

Sample snippet contributions

For client library sample snippets, review and follow the snippet contribution guidance

• [ ] Follow organization guidelines
• [ ] Use real types (avoids var)
• [ ] Use Context.Log (avoids Console.WriteLine)
• [ ] Sample should clean up resources they create
• [ ] Avoid samples that arbitrarily destroy data

[vtbassmatt]

If you'll retarget this PR at main, I'll merge it. Thanks!

[adriennetacke]

Thanks for the heads up! just retargeted to main :)