Improve documentation around user registration (#13640)

Update a bunch of the documentation for user registration, add some cross
links, etc.

1 files changed, 14 insertions, 9 deletions

diff --git a/docs/setup/installation.md b/docs/setup/installation.md
index 260e50577b..bb78b3267a 100644
--- a/docs/setup/installation.md
+++ b/docs/setup/installation.md
@@ -506,9 +506,13 @@ email will be disabled.
 
 ### Registering a user
 
-The easiest way to create a new user is to do so from a client like [Element](https://element.io/).
+One way to create a new user is to do so from a client like
+[Element](https://element.io/).  This requires registration to be enabled via
+the
+[`enable_registration`](../usage/configuration/config_documentation.md#enable_registration)
+setting.
 
-Alternatively, you can do so from the command line. This can be done as follows:
+Alternatively, you can create new users from the command line. This can be done as follows:
 
  1. If synapse was installed via pip, activate the virtualenv as follows (if Synapse was
     installed via a prebuilt package, `register_new_matrix_user` should already be
@@ -520,7 +524,7 @@ Alternatively, you can do so from the command line. This can be done as follows:
     ```
  2. Run the following command:
     ```sh
-    register_new_matrix_user -c homeserver.yaml http://localhost:8008
+    register_new_matrix_user -c homeserver.yaml
     ```
 
 This will prompt you to add details for the new user, and will then connect to
@@ -533,12 +537,13 @@ Make admin [no]:
 Success!
 ```
 
-This process uses a setting `registration_shared_secret` in
-`homeserver.yaml`, which is shared between Synapse itself and the
-`register_new_matrix_user` script. It doesn't matter what it is (a random
-value is generated by `--generate-config`), but it should be kept secret, as
-anyone with knowledge of it can register users, including admin accounts,
-on your server even if `enable_registration` is `false`.
+This process uses a setting
+[`registration_shared_secret`](../usage/configuration/config_documentation.md#registration_shared_secret),
+which is shared between Synapse itself and the `register_new_matrix_user`
+script. It doesn't matter what it is (a random value is generated by
+`--generate-config`), but it should be kept secret, as anyone with knowledge of
+it can register users, including admin accounts, on your server even if
+`enable_registration` is `false`.
 
 ### Setting up a TURN server