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/ospfd.texi b/doc/ospfd.texi
index 7ddc9db..86cabe4 100644
--- a/doc/ospfd.texi
+++ b/doc/ospfd.texi
@@ -11,6 +11,7 @@
 networks.
 
 @menu
+* OSPF Fundamentals::
 * Configuring ospfd::           
 * OSPF router::                 
 * OSPF area::                   
@@ -21,6 +22,8 @@
 * OSPF Configuration Examples::
 @end menu
 
+@include ospf_fundamentals.texi
+
 @node Configuring ospfd
 @section Configuring ospfd