doc: Add 'OSPF Fundamentals' section to OSPF docs

* ospf_fundamentals.texi: New section explaining the fundamentals of OSPF
  for system admins, to help them debug their networks.
* {Makefile.am,ospfd.texi}: include and build previous

Conflicts:
	doc/Makefile.am
diff --git a/doc/Makefile.am b/doc/Makefile.am
index 3ff3170..943f06b 100644
--- a/doc/Makefile.am
+++ b/doc/Makefile.am
@@ -50,7 +50,7 @@
 	install.texi ipv6.texi kernel.texi main.texi ospf6d.texi ospfd.texi \
 	overview.texi protocol.texi ripd.texi ripngd.texi routemap.texi \
 	snmp.texi vtysh.texi routeserver.texi defines.texi $(figures_png) \
-	snmptrap.texi $(figures_txt)
+	snmptrap.texi ospf_fundamentals.texi $(figures_txt)
 
 .png.eps:
 	$(PNGTOEPS) $< "$@"