tftp script: "#!/bin/sh" is now mandatory

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>

binaries/wrboot-dhcp

+#!/bin/sh
+
 bootargs="quiet console=ttyS0,115200 panic=10 mem=64m"
 bootargs="$bootargs root=nfs ip=dhcp"
 

binaries/wrboot-static-ip

+#!/bin/sh
+
 bootargs="quiet console=ttyS0,115200 panic=10 mem=64m"
 bootargs="$bootargs root=nfs ip=192.168.16.9:192.168.16.1:255.255.255.0"
 

doc/wrs-build.in

@@ -918,6 +918,10 @@ this is the default place where the NFS-Root filesystem is mounted
 from, as shown in the log excerpt above. So you'll have your
 @file{wrboot} in the same place
 
+@b{Note:} recent @i{barebox} versions require scripts to include a
+leading @t{#!/bin/sh}. Examples in @i{wr-switch-sw} did not include the
+line until April 2014 included.
+
 The @file{binaries} subdirectory of this package includes two known-working
 wrboot scripts as examples; one if for use with static IP addresses and
 the other relies on DHCP. If you want to override the default NFS-Root