Add custom domains guide

content/guides/custom-domains.md

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+---
+title: Custom Domains Guide
+---
+
+So you want to point a custom domain at takahe.social? Great! Before you start,
+you need to understand a few things:
+
+* Custom domains are limited and available by request only. Email
+  contact@jointakahe.org to request one; we may or may not have capacity.
+  Each custom domain is administrative and operational overhead for us.
+
+* Once you make accounts (identities) on your custom domain, you will not be
+  able to move them away from takahe.social until we implement the move
+  feature in the future. Even then, your posts will not follow you, only
+  your followers.
+
+* Custom domains are not separate servers - you will still be on the same
+  "server" as everyone else, see everyone else in the Local feeds, use our
+  global set of server emoji, and be subject to our moderation policies and
+  rules.
+
+If you're alright with that, then let's discuss how to set up your domain.
+
+There's two ways you can route a domain to us:
+
+* Pointing the whole domain at takahe.social. This is the easiest way, but
+  it means you will not be able to use that domain for anything else
+  (for example, if you want `@user@sub.domain.tld` to be your handle, you must
+  point the entirely of `sub.domain.tld` at us and nothing else can exist on it).
+
+* Routing users from a main domain to a Takahē-specific subdomain.
+  This is generally preferred, as it lets you have `@user@domain.tld` work, while
+  still serving a different website on `domain.tld`. Takahē will serve requests
+  from a subdomain like `takahe.domain.tld`.
+
+Please understand that once you have selected one of these options it
+**cannot be changed** without you losing all your follows. Unless you are very
+sure what you are doing, **we suggest using a Takahē-specific subdomain**.
+
+You will be able to log into Takahē using the same credentials either at
+[takahe.social](https://takahe.social) or under your custom domain; it will
+work the same either way.
+
+
+## Whole Domain
+
+To point a whole domain at us, you need to add a DNS CNAME from that domain
+to `takahe.social`.
+
+If you are trying to point an apex domain that does not
+support CNAMEs, you can make an A record that points to our IP address
+of `104.198.180.195`. This IP may change as we get our network setup fully
+stabilised; we will try and let you know via email when this is going to
+happen.
+
+Note that no subdomains of the domain you provide will work, not even `www`,
+as we will only issue an SSL certificate for the exact one you provide.
+
+
+## Takahē-Specific Subdomain
+
+To point a subdomain at us, you will need to add a DNS CNAME for it to
+`takahe.social`.
+
+If you then want account handles to work off of your main domain, you will
+need to proxy through these URLs from that main domain to the subdomain:
+
+* `/.well-known/webfinger`
+* `/.well-known/host-meta`
+* `/.well-known/nodeinfo`