fio2gnuplot: Adding manpage

As requested by users, let's add a manpage to make things easier to
understand.

I'm providing here the raw file used to generate the manpage. It can be
converted to a real manpage by using txt2man.

I'm also providing the manpage file to avoid dependencies at build time,
anyway the makefile target can be easily used to rebuild it if
necessary.
diff --git a/Makefile b/Makefile
index 31cd371..eb0e892 100644
--- a/Makefile
+++ b/Makefile
@@ -275,11 +275,15 @@
 cscope:
 	@cscope -b -R
 
-install: $(PROGS) $(SCRIPTS) FORCE
+tools/plot/fio2gnuplot.1:
+	@cat tools/plot/fio2gnuplot.manpage | txt2man -t fio2gnuplot >  tools/plot/fio2gnuplot.1
+
+install: $(PROGS) $(SCRIPTS) tools/plot/fio2gnuplot.1 FORCE
 	$(INSTALL) -m 755 -d $(DESTDIR)$(bindir)
 	$(INSTALL) $(PROGS) $(SCRIPTS) $(DESTDIR)$(bindir)
 	$(INSTALL) -m 755 -d $(DESTDIR)$(mandir)/man1
 	$(INSTALL) -m 644 fio.1 $(DESTDIR)$(mandir)/man1
 	$(INSTALL) -m 644 tools/fio_generate_plots.1 $(DESTDIR)$(mandir)/man1
+	$(INSTALL) -m 644 tools/plot/fio2gnuplot.1 $(DESTDIR)$(mandir)/man1
 	$(INSTALL) -m 755 -d $(DESTDIR)$(sharedir)
 	$(INSTALL) -m 644 tools/plot/*gpm $(DESTDIR)$(sharedir)/