Reword introductions to Keycloak's documentation

I think it's a little clearer this way what Keycloak is
and when a reader should care (or not) about it.

docs/index.rst

@@ -29,7 +29,8 @@ Architecture
   architecture
 * :ref:`mirror` → learn what a Software Heritage mirror is and how to set up
   one
-* :ref:`keycloak <keycloak>` → learn what keycloak is and how to register and configure users
+* :ref:`Keycloak <keycloak>` → learn how to use Keycloak,
+  the authentication system used by |swh|'s web interface and public APIs
 
 Data Model and Specifications
 -----------------------------

docs/keycloak/index.rst

@@ -11,7 +11,9 @@ Keycloak
 
 Software Heritage uses `Keycloak <https://www.keycloak.org/>`__, an open
 source identity and access management solution, to identify and
-authenticate users on its services (for instance the Web API).
+authenticate users on its services (for instance the
+`archive's Web API <https://archive.softwareheritage.org/api/>`_
+and the :ref:`deposit server <swh-deposit>`).
 
 Keycloak implements the `OpenID Connect <https://openid.net/connect/>`__
 specification, a simple identity layer on top of the OAuth 2.0 protocol.