diff --git a/docs/config.md b/docs/config.md
index 6bcb1b6f93..55b77849c4 100644
--- a/docs/config.md
+++ b/docs/config.md
@@ -1,8 +1,12 @@
 # Configuration
 
-You can configure the app by copying `config.sample.json` to `config.json` and customising it. The possible options are
-described here. If you run into issues, please visit [#element-web:matrix.org](https://matrix.to/#/#element-web:matrix.org)
-on Matrix.
+You can configure the app by copying `config.sample.json` to `config.json` or `config.$domain.json` and customising it.
+Element will attempt to load first `config.$domain.json` and if it fails `config.json`. This mechanism allows different
+configuration options depending on if you're hitting e.g. `app1.example.com` or `app2.example.com`. Configs are not mixed
+in any way, it either entirely uses the domain config, or entirely uses `config.json`.
+
+The possible configuration options are described here. If you run into issues, please visit
+[#element-web:matrix.org](https://matrix.to/#/#element-web:matrix.org) on Matrix.
 
 For a good example of a production-tuned config, see https://app.element.io/config.json