[libxmlplusplus] Update README

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 78c2fefaaf2bb9f79e7879f17c8bcdae887182ac
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Sat Jul 14 10:58:57 2018 +0200

    Update README

 README | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/README b/README
index cb4ff96..8846c38 100644
--- a/README
+++ b/README
@@ -17,5 +17,5 @@ See the examples directory for example code.
 
 Use pkg-config to discover the necessary include and linker arguments. For
 instance,
-  pkg-config libxml++-3.0 --cflags --libs
+  pkg-config libxml++-4.0 --cflags --libs
 Ideally you would use PKG_CHECK_MODULES in your configure.ac file.