Added doc node about usage across differen top routes.

Related to #1277 report

(cherry picked from commit fefc33f)

modules/benchmark/README

@@ -93,6 +93,15 @@ Chapter 1. Admin Guide
    that all durations are given as microseconds (don't confuse
    with milliseconds!).
 
+   Important note: as this benchmarking is intended to measure the
+   time spent in executing different parts/blocks of the script
+   (and not for measuring the time induced by the SIP signaling),
+   the benchmark module is to be used within the SAME top route
+   (request route, failure route, branch route, onreply rout,
+   etc). It is not design to be used across different types of top
+   routes (like started in request route and ended in failure
+   route)!!
+
 1.2. Dependencies
 
 1.2.1. OpenSIPS Modules

modules/benchmark/doc/benchmark_admin.xml

@@ -16,6 +16,14 @@
 		via &osips;'s logging facility. Please note that all durations are given as
 		microseconds (don't confuse with milliseconds!).
 	</para>
+	<para> Important note: as this benchmarking is intended to measure the time
+		spent in executing different parts/blocks of the script (and not for 
+		measuring the time induced by the SIP signaling), the benchmark module
+		is to be used within the SAME top route (request route, failure route, 
+		branch route, onreply rout, etc). It is not design to be used across 
+		different types of top routes (like started in request route and ended in 
+		failure route)!!
+	</para>
 	</section>
 	<section>
 	<title>Dependencies</title>