[diff.class] Move text into note

Author: Andreas-Krug

source/compatibility.tex

@@ -3628,8 +3628,10 @@
 All the definitions of C struct types enclosed in other struct
 definitions and accessed outside the scope of the enclosing
 struct can be exported to the scope of the enclosing struct.
-Note: this is a consequence of the difference in scope rules,
+\begin{note}
+This is a consequence of the difference in scope rules,
 which is documented in \ref{basic.scope}.
+\end{note}
 \howwide
 Seldom.