docs: install: recommend gnuplot for ifpps

ifpps supports a gnuplot-like output. Therefore, recommend the use
of gnuplot. It is not mandatory though.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/INSTALL b/INSTALL
index f2deb5d..8fc0736 100644
--- a/INSTALL
+++ b/INSTALL
@@ -34,6 +34,7 @@ What additional tools are recommended, but not mandatory after the build?
 
  - cpp:			   trafgen
  - ntpd:		   curvetun
+ - gnuplot:		   ifpps
  - setcap:		   all
 
 It is common, that these libraries are shipped as distribution packages