[diff.cpp20,diff.cpp17] Add missing inclusion clause

Author: jensmaurer

source/compatibility.tex

@@ -241,6 +241,7 @@
 \indextext{summary!compatibility with ISO \CppXX{}}%
 Subclause \ref{diff.cpp20} lists the differences between \Cpp{} and
 ISO \CppXX{},
+in addition to those listed above,
 by the chapters of this document.
 
 \rSec2[diff.cpp20.lex]{\ref{lex}: lexical conventions}
@@ -598,6 +599,7 @@
 \indextext{summary!compatibility with ISO \CppXVII{}}%
 Subclause \ref{diff.cpp17} lists the differences between \Cpp{} and
 ISO \CppXVII{},
+in addition to those listed above,
 by the chapters of this document.
 
 \rSec2[diff.cpp17.lex]{\ref{lex}: lexical conventions}