reference to nanocat added to nanomsg(7)

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>
diff --git a/doc/nanomsg.txt b/doc/nanomsg.txt
index d548a7a..0d94c65 100644
--- a/doc/nanomsg.txt
+++ b/doc/nanomsg.txt
@@ -105,6 +105,10 @@
 TCP transport::
     linknanomsg:nn_tcp[7]
 
+Following tools are installed with the library:
+
+nanocat::
+    linknanomsg:nanocat[1]
 
 AUTHORS
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