add scripts/git.orderfile

Based on a old patch by Laszlo.
Time to get this in ...

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Emilio G. Cota <cota@braap.org>
Message-id: 20170717101632.23247-1-kraxel@redhat.com

scripts/git.orderfile

+#
+# order file for git, to produce patches which are easier to review
+# by diffing the important stuff like interface changes first.
+#
+# one-off usage:
+#   git diff -O scripts/git.orderfile ...
+#
+# add to git config:
+#   git config diff.orderFile scripts/git.orderfile
+#
+
+# Documentation
+docs/*
+*.texi
+
+# build system
+configure
+Makefile*
+*.mak
+
+# qapi schema
+*.json
+
+# headers
+*.h
+
+# code
+*.c
+