add url to the wikipedia article for a longer description

docs/libcurl/ABI

@@ -6,13 +6,16 @@
 
                           libcurl's binary interface
 
-ABI
+ABI - Application Binary Interface
 
   First, allow me to define the word for this context: ABI describes the
   low-level interface between an application program a library. Calling
   conventions, function arguments, return values, struct sizes/defines and
   more.
 
+  For a longer descricption, see
+  http://en.wikipedia.org/wiki/Application_binary_interface
+
 Upgrades
 
   In the vast majority of all cases, a typical libcurl upgrade does not break