doc: Fix a doxygen warning

Signed-off-by: Andreas Schneider <asn@cryptomilk.org>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>

doc/linking.dox

@@ -28,6 +28,6 @@ the dllimport attribute.
 @endcode
 
 If you're are statically linking with OpenSSL, read the "Linking your
-application" section in the NOTES.<OS> in the OpenSSL source tree!
+application" section in the NOTES.[OS] in the OpenSSL source tree!
 
 */