Migrate README content to dev docs

[chadwhitacre]

Silly and confusing to have two sources of truth. Let's consolidate on dev docs.

https://github.com/getsentry/self-hosted#readme ⇒
https://develop.sentry.dev/self-hosted/

[github-actions]

This issue has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you label it Status: Backlog or Status: In Progress, I will leave it alone ... forever!

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"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀

[aldy505]

Me and @BYK talked about this a while ago on Discord (link https://discord.com/channels/621778831602221064/796028405833007104/1250449735815401704) since we have two docs in which I think people don't really read the docs on the develop website.

So what I wonder about are:

1. Which part of the self-hosted documentation should we sync, between the develop docs site and the repo's README?
2. Or.. should we nuke the README on the repository and point people to go to the website? But I don't think this route is a good idea.

cc @hubertdeng123 @azaslavsky