docs(replay): Update replay README

[mydea]

Related to #6383, this PR improves & updates the docs for replay.

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1. Updates the docs for how to define the sample rate(s)
2. Add maskTextSelector documentation
3. Add section about how errors are linked to replays
4. Section docs into where configuration has to go, for clarity
5. For now, the rrweb config stuff remains as is. If/when we do [Replay] Move rrweb-specific configuration into recordingOptions #6390, we can update this accordingly.

[Lms24]

Nice work! One additional suggestion:

We could copy over the Sentry logo and badges (they should work ootb if you just rename the package name in the links) from another package (e.g. Integrations).

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	19.6 KB (0%)
@sentry/browser - ES5 CDN Bundle (minified)	60.69 KB (0%)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	18.37 KB (+0.02% 🔺)
@sentry/browser - ES6 CDN Bundle (minified)	54.26 KB (0%)
@sentry/browser - Webpack (gzipped + minified)	20.13 KB (0%)
@sentry/browser - Webpack (minified)	65.83 KB (0%)
@sentry/react - Webpack (gzipped + minified)	20.16 KB (0%)
@sentry/nextjs Client - Webpack (gzipped + minified)	46.96 KB (0%)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	26.44 KB (0%)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	24.87 KB (+0.02% 🔺)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	41.74 KB (0%)
@sentry/replay - Webpack (gzipped + minified)	37.23 KB (0%)