doc: improve wording of Error Message Style Guide

Reported-by: Daniel Gustafsson

Discussion: 48DB4EDA-96F8-4B2F-99C4-110900FC7540@yesql.se

Author: Daniel Gustafsson

doc/src/sgml/sources.sgml

@@ -453,7 +453,7 @@ Hint:       the addendum
     verbose mode, or perhaps a pop-up error-details window.  Also, details and
     hints would normally be suppressed from the server log to save
     space. Reference to implementation details is best avoided since users
-    don't know the details anyway.
+    aren't expected to know the details.
    </para>
 
   </simplesect>