tracing: Add inter-event blurb to HIST_TRIGGERS config option

So that users know that inter-event tracing is supported as part of
the HIST_TRIGGERS option, include text to that effect in the help
text.

Link: http://lkml.kernel.org/r/a38e24231d8d980be636b56d35814570acfd167a.1516069914.git.tom.zanussi@linux.intel.com

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/Kconfig

@@ -606,7 +606,10 @@ config HIST_TRIGGERS
 	  event activity as an initial guide for further investigation
 	  using more advanced tools.
 
-	  See Documentation/trace/events.txt.
+	  Inter-event tracing of quantities such as latencies is also
+	  supported using hist triggers under this option.
+
+	  See Documentation/trace/histogram.txt.
 	  If in doubt, say N.
 
 config MMIOTRACE_TEST