docs: small spelling fix (bellow -> below)

doc/tutorials/seruser/intro.xml

@@ -1271,7 +1271,7 @@ route{
 		For example, we use the UA functionality to shield 
 		SMS gateway and instant message store from SIP transactional
 		processing.
-		The simple example bellow issues a log report on receipt
+		The simple example below issues a log report on receipt
 		of a new transaction. 
 		If we did not use a stateful UA, every single request retransmission
 		would cause the application to be re-executed which would result in

doc/tutorials/seruser/operation.xml

@@ -417,7 +417,7 @@ warning: IP extract from warning activated to be more informational
 					    </programlisting>
 					    <para>
 						The following SIP message causes then logging output as shown
-						bellow.
+						below.
 					    </para>
 					    <programlisting>
 REGISTER sip:192.168.2.16 SIP/2.0