add to dist: doc subdir with all current doc files

Change-Id: Idfef4f050e21a5d0eae3a530fe319a5adf81534d
diff --git a/doc/Makefile.am b/doc/Makefile.am
new file mode 100644
index 0000000..6974e89
--- /dev/null
+++ b/doc/Makefile.am
@@ -0,0 +1,10 @@
+EXTRA_DIST = \
+  hnb_cs_lu.msc \
+  hnb_cs_mo_call.msc \
+  hnb_cs_mo_sms.msc \
+  hnb_cs_mt_call.msc \
+  hnb_cs_mt_sms.msc \
+  hnb_ps_lu.msc \
+  hnb_ps_pdp_act.msc \
+  protocols_around_hnbgw.txt \
+  README