docs: add docs around improving compile times

documentation/topics/compile_times.md

@@ -0,0 +1,43 @@
+# Improving Compile Times
+
+In previous versions of Ash, the standard way to configure the list of resources for an Api module looked like this:
+
+```elixir
+defmodule MyApp.MyApi do
+  use Ash.Api
+
+
+  resources do
+    resource MyApp.MyResource
+    ...
+  end
+end
+```
+
+This caused many compilation dependency issues, causing slow compile times when changing single files, and could also potentially lead to deadlocks.
+
+The preferred way of doing this now looks like this:
+
+```elixir
+# Define a registry module
+defmodule MyApp.MyApi.Registry do
+  use Ash.Registry,
+    extensions: Ash.Registry.ResourceValidations
+
+  registry do
+    entry MyApp.MyResource
+    ...
+  end
+end
+
+defmodule MyApp.MyApi do
+  use Ash.Api, otp_app: :my_app
+end
+
+# in `config/config.exs`
+
+config :my_app, MyApp.MyApi,
+  registry: MyApp.MyApi.Registry
+```
+
+This will prevent a bunch of cross-concern compile time dependencies, allowing for much faster compile times in general.

mix.exs

@@ -85,6 +85,9 @@ defmodule Ash.MixProject do
         ],
         "documentation/topics/multitenancy.md": [
           title: "Multitenancy"
+        ],
+        "documentation/topics/compile_times.md": [
+          title: "Compile Times"
         ]
       ],
       groups_for_extras: [