KEYCLOAK-1404: Need recovery mechanism for master admin user

docbook/reference/en/en-US/master.xml

@@ -35,6 +35,7 @@
                 <!ENTITY UserFederation SYSTEM "modules/user-federation.xml">
                 <!ENTITY Kerberos SYSTEM "modules/kerberos.xml">
                 <!ENTITY ExportImport SYSTEM "modules/export-import.xml">
+                <!ENTITY AdminRecovery SYSTEM "modules/admin-recovery.xml">
                 <!ENTITY ServerCache SYSTEM "modules/cache.xml">
                 <!ENTITY SecurityVulnerabilities SYSTEM "modules/security-vulnerabilities.xml">
                 <!ENTITY Clustering SYSTEM "modules/clustering.xml">
@@ -126,6 +127,7 @@ This one is short
     &UserFederation;
     &Kerberos;
     &ExportImport;
+    &AdminRecovery;
     &ServerCache;
     &SAML;
     &SecurityVulnerabilities;

docbook/reference/en/en-US/modules/admin-recovery.xml

@@ -0,0 +1,15 @@
+<chapter id="admin-recovery">
+    <title>Recovering the Master Admin User</title>
+    <para>
+        It is possible for the "admin" user in the master realm to become inoperable.  This may be because it was
+        accentally deleted, its role mappings were removed, or the password was simply forgotten.
+    </para>
+    <para>
+        To recover the master admin user, just start the server with the following system property:
+        <programlisting><![CDATA[
+bin/standalone.sh -Dkeycloak.recover-admin=true
+]]></programlisting>
+        Then you can log in to the master admin account with the default password "admin".  You will then be
+        prompted to immediately change this password.
+    </para>
+</chapter>