Fix compilation error in code example

Author: zoffixznet

doc/Type/Telemetry/Instrument/Usage.pod6

@@ -52,6 +52,7 @@ The following readings may or may not contain sensible information, mostly
 depending on hardware and OS being used.  Please check your local C<getrusage>
 documentation for their exact meaning:
 
+  =begin code :lang<text>
   name        getrusage struct name
   ====        =====================
   max-rss     ru_maxrss
@@ -68,6 +69,7 @@ documentation for their exact meaning:
   nsig        ru_nsignals
   volcsw      ru_nvcsw
   invcsw      ru_nivcsw
+  =end code
 
 =end pod