Skeleton for User directory setup instructions

docs/features/directory-users.md

@@ -0,0 +1,14 @@
+- Only work for LDAP and SQL
+  - For LDAP: Set LDAP config (new global filter, optional: threepids attributes if the default identity queries were changed)
+  - For SQL: Use `synapseSql` module with `type: {sqlite|postgresql}` and `database` as JDBC url after `jdbc:driver:`
+    - `/path/to/db` for `sqlite`
+    - `//host/db?username...` for `postgresql`)
+- Configure DNS overwrite for domain name (and mention ${matrix.domain} can be used)
+```
+dns.overwrite.homeserver.client:
+  - name: 'example.org'
+    value: 'http://localhost:8008'
+```
+- Configure reverse proxy
+  - for `/_matrix/client/r0/user_directory/search` to `http://internalIp:8008/_matrix/client/r0/user_directory/search`
+  - With `ProxyPreserveHost on` on apache