[temp.mem.func] Add introductory text to new example to separate it from the prior example.

Author: zygoloid

source/templates.tex

@@ -2226,6 +2226,7 @@
 }
 \end{codeblock}
 
+A constrained member function can be defined out of line:
 \begin{codeblock}
 template<typename T> concept C = requires {
   typename T::type;