man: rtpr: add minimal manpage

While there is not much to explain about this rather trivial shell
script, having a manpage for it serves as good point of reference for
users wondering what it might be for.
Signed-off-by: Phil Sutter <phil@nwl.cc>

man/man8/Makefile

 TARGETS = ip-address.8 ip-link.8 ip-route.8
 
-MAN8PAGES = $(TARGETS) ip.8 arpd.8 lnstat.8 routel.8 rtacct.8 rtmon.8 ss.8 \
+MAN8PAGES = $(TARGETS) ip.8 arpd.8 lnstat.8 routel.8 rtacct.8 rtmon.8 rtpr.8 ss.8 \
 	tc.8 tc-bfifo.8 tc-bpf.8 tc-cbq.8 tc-cbq-details.8 tc-choke.8 tc-codel.8 \
 	tc-drr.8 tc-ematch.8 tc-fq_codel.8 tc-hfsc.8 tc-htb.8 tc-pie.8 \
 	tc-mqprio.8 tc-netem.8 tc-pfifo.8 tc-pfifo_fast.8 tc-prio.8 tc-red.8 \

man/man8/rtpr.8

+.TH RTPR 8 "18 September, 2015"
+
+.SH NAME
+rtpr \- replace backslashes with newlines.
+
+.SH DESCRIPTION
+.B rtpr
+is a trivial bash script which converts backslashes in standard input to newlines. It's sole purpose is to be fed with input from
+.B ip
+when executed with it's
+.B --oneline
+flag.
+
+.SH EXAMPLES
+.TP
+ip --onenline address show | rtpr
+Undo oneline converted
+.B ip-address
+output.
+
+.SH SEE ALSO
+.BR ip (8)
+
+.SH AUTHORS
+Stephen Hemminger <shemming@brocade.com>