docs(replay): Add CDN bundle instructions to README

[Lms24]

This PR adds a subsection about CDN bundle installation and usage.

The only thing that's different in this doc compared to a normal integration CDN bundle doc on Sentry docs is that I can't specify the integrity attribute in the script tag because we can't automatically get the correct checksum in the Readme. I opted to leave it out and add a sentence that links people to our CDN bundle checksum table.

internal ref: https://www.notion.so/sentry/Checklist-Closed-Beta-Cohort-2-db73b0edc8e84fd28e6fc8253b79469f

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	19.67 KB (-0.02% 🔽)
@sentry/browser - ES5 CDN Bundle (minified)	60.94 KB (0%)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	18.46 KB (0%)
@sentry/browser - ES6 CDN Bundle (minified)	54.49 KB (0%)
@sentry/browser - Webpack (gzipped + minified)	20.26 KB (0%)
@sentry/browser - Webpack (minified)	66.24 KB (0%)
@sentry/react - Webpack (gzipped + minified)	20.29 KB (0%)
@sentry/nextjs Client - Webpack (gzipped + minified)	47.14 KB (0%)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	26.52 KB (0%)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	24.96 KB (+0.02% 🔺)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	41.73 KB (-0.52% 🔽)
@sentry/replay - Webpack (gzipped + minified)	37.82 KB (-0.19% 🔽)

[mydea]

🚀

[Lms24]

Merging this now to get it into the release. @reviewers, if you have comments/suggestions, we can open a follow-up PR and address them there