docs(vercel-edge): Update @sentry/vercel-edge readme to remove alpha status and clarify usage recommendations

[lforst]

We want to remove the alpha status of this package but also tell users not to depend on this package directly, as we would like to reserve the right to break it.

By removing the usage instructions I want to discourage people from actually using this package directly.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser	22.5 KB (0%)
@sentry/browser (incl. Tracing)	34.3 KB (0%)
@sentry/browser (incl. Tracing, Replay)	70.52 KB (0%)
@sentry/browser (incl. Tracing, Replay) - with treeshaking flags	63.83 KB (0%)
@sentry/browser (incl. Tracing, Replay with Canvas)	74.91 KB (0%)
@sentry/browser (incl. Tracing, Replay, Feedback)	87.54 KB (0%)
@sentry/browser (incl. Tracing, Replay, Feedback, metrics)	89.36 KB (0%)
@sentry/browser (incl. metrics)	26.81 KB (0%)
@sentry/browser (incl. Feedback)	39.47 KB (0%)
@sentry/browser (incl. sendFeedback)	27.13 KB (0%)
@sentry/browser (incl. FeedbackAsync)	31.79 KB (0%)
@sentry/react	25.26 KB (0%)
@sentry/react (incl. Tracing)	37.29 KB (0%)
@sentry/vue	26.65 KB (0%)
@sentry/vue (incl. Tracing)	36.14 KB (0%)
@sentry/svelte	22.64 KB (0%)
CDN Bundle	23.73 KB (0%)
CDN Bundle (incl. Tracing)	35.97 KB (0%)
CDN Bundle (incl. Tracing, Replay)	70.36 KB (0%)
CDN Bundle (incl. Tracing, Replay, Feedback)	75.6 KB (0%)
CDN Bundle - uncompressed	69.61 KB (0%)
CDN Bundle (incl. Tracing) - uncompressed	106.54 KB (0%)
CDN Bundle (incl. Tracing, Replay) - uncompressed	218.05 KB (0%)
CDN Bundle (incl. Tracing, Replay, Feedback) - uncompressed	230.94 KB (0%)
@sentry/nextjs (client)	37.16 KB (+0.04% 🔺)
@sentry/sveltekit (client)	34.9 KB (0%)
@sentry/node	115.61 KB (0%)
@sentry/node - without tracing	90 KB (0%)
@sentry/aws-serverless	99.42 KB (0%)