add line

omero/sysadmins/config.rst

@@ -2052,6 +2052,7 @@ Whether to ignore the case of the username during login (`true` or
 `false`). Default: `false` (JSmith and jsmith will be considered two
 different users).
 .. warning::
+
    Before enabling this feature, lower the case of all usernames in OMERO
    (`omename` column in the `experimenter` table). It is the system
    administrator's responsibility to handle any username clashes.