configure: Use PKG_PROG_PKG_CONFIG + mention pkg-config dep in README

README

@@ -26,14 +26,14 @@ INSTALL
     make install
 
   If you're building directly from the git repository, make sure you have perl
-  (or rather, pod2man) and GNU autoconf/automake installed, then run
-  'autoreconf -i', and you're ready to continue with the usual ./configure and
-  make route.
+  (or rather, pod2man), pkg-config and GNU autoconf/automake installed, then
+  run 'autoreconf -i', and you're ready to continue with the usual ./configure
+  and make route.
 
 
 COPYING
 
-  Copyright (c) 2007-2012 Yoran Heling
+  Copyright (c) 2007-2013 Yoran Heling
 
   Permission is hereby granted, free of charge, to any person obtaining
   a copy of this software and associated documentation files (the

configure.ac

@@ -8,6 +8,7 @@ AM_INIT_AUTOMAKE([foreign subdir-objects])
 AC_PROG_CC
 AC_PROG_INSTALL
 AC_PROG_RANLIB
+PKG_PROG_PKG_CONFIG
 
 # Check for header files.
 AC_CHECK_HEADERS(