[support.types.layout] Avoid implementation guidance in a note

Turn it into a "recommended practice" section.

Author: jensmaurer

source/support.tex

@@ -326,11 +326,10 @@
 to contain the size in bytes of any object\iref{expr.sizeof}.
 
 \pnum
-\begin{note}
-It is recommended that implementations choose types for \tcode{ptrdiff_t} and \tcode{size_t}
+\recommended
+An implementation should choose types for \tcode{ptrdiff_t} and \tcode{size_t}
 whose integer conversion ranks\iref{conv.rank} are no greater than that of
 \tcode{signed long int} unless a larger size is necessary to contain all the possible values.
-\end{note}
 
 \pnum
 The type