Improve end-user documentation/deployment

[codesections]

Before releasing version 1.0.0, we should ensure that we have good documentation on how sysadmins can deploy and configure Flodgatt. I believe we'll need:

• A revised README
• cargo doc generated documentation on all runtime options (this could live in the README, but keeping the docs with the code is best practice and will help ensure that there isn't any doc drift.
• Updates to the Mastodon docs on the streaming API and on installing Mastodon.
• A docker-compose file (maybe we can just use the one in Opt-In Flodgatt in docker-compose.yml mastodon#13286?)
• A systemd unit file.
• An announcement blog post

For the blog post, I'm not sure if it makes sense to post something to the Mastodon blog; if not, I'll at least post something to my personal blog. Either way, it would be great to have some before-and-after numbers to show a nice comparison. The Internet loves a good benchmark and a good rewrite-it-in-Rust story. Since this is both, it might be able to get Mastodon another burst of attention.