netboot: mg-netgrub-loader-update: Add some more docs

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>

diff --git a/mg-netgrub-loader-update b/mg-netgrub-loader-update
index 73deb19f6ba192c5958e05a4b017db83cd2429b8..22ef67c29416c945054f63520489a1b6fd5788c1 100755 (executable)
--- a/mg-netgrub-loader-update
+++ b/mg-netgrub-loader-update
@@ -10,6 +10,18 @@
 # (where EE:EE:EE:EE:EE:EE is the MAC address)
 # (or whatever else is specified in TftpNetGrubTemplates).
 
+# Running this script is optional.  Any approach will do which
+# arranges for the dhcp server to provide `filename' referring to a
+# copy of grub which will eventually load the config file specified by
+# TftpNetGrubPattern.  An example would be an appropriate
+# debian-installer netboot grub image, which will load 
+#   $c{TftpPath}/debian-installer/arm64/grub/grub.cfg
+# which could for example be made to contain
+#   configfile Netgrub.cfg/${net_default_mac}
+
+# This script does not currently support non-default Tftp scopes.
+# (See README.)
+
 # This is part of "osstest", an automated testing framework for Xen.
 # Copyright (C) 2015 Citrix Inc.
 #