* Fix crowdin badge display in CONTRIBUTING.md
The Crowdin localization badge in `CONTRIBUTING.md` appeared to have the wrong markup around it. This manifested in some extra brackets and an unformatted `crowdin` string.
* Make Crowdin badge a link to the Mastodon project
* Remove docker guide and put it in docs repo
* Move tasks to docs repo
* Move requirements to contributing doc
* Move advice about tagged releases to docs repo
* Move local domain and host config to docs repo
* Link to related tech