[matrix] Document user registration.

diff --git a/matrix/README b/matrix/README
index 4ace5857a74f0a0debe47f5ef557e782058aa944..315bc49e4ed57a2e6e47ea850cd5dbcd2f6d0d57 100644 (file)
--- a/matrix/README
+++ b/matrix/README
@@ -34,3 +34,14 @@ Install
 ```
 $ apt install matrix-synapse
 ```
+
+Users
+-----
+
+Matrix requires a shared secret to create a user. It can placed in a separate
+file `/etc/matrix-synapse/conf.d/shared_secret.yaml`.
+
+```
+synapse_register_new_matrix_user -u <name> \
+  -c /etc/matrix-synapse/conf.d/shared_secret.yaml
+```