Rewrite Collection Documentation and Tutorial

[maxhoesel]

As part of the 1.x release, this collections docs could use an overhaul.

Right now, pretty much all of the general documentation is in the README.md, which makes the file long and difficult to read.
At the same time, many details aren't elaborated on and the step-by-step guide has not been updated in a while.

To bring the docs up to a standard deserving of a 1.x release, the following changes should be made:

• Clean out the README - split out the step-by-step guide (preferably into a separate docs RST) and make the components overview more compact
• Update the role docs to mention supported distributions explicitly, instead of saying "x and up"
• Rewrite the step-by-step guide to be more thorough
  • Document the different approaches to certificate renewal and their pros/cons, specifically:
    • Using the step_ca_certificate module with renew (see step_ca_certificate: add state parameter #188)
    • Using the step_acme_cert role or its successor (see role to support JWK-based (x509) certificates #127 and step_acme_cert: Replace with a more generic host-autorenewal-certificate role #339)
    • Using ACME on the CA with certbot, Caddy, etc
  • Include remote provisioner and admin usage once Support remote provisioner management #141 gets resolved
• Rewrite the module usage to be more clear about offline vs online usage