Add note that the various \see* macros are only defined in the context

of a seealso environment.

Doc/doc/doc.tex

@@ -808,6 +808,9 @@ distribution, to create or maintain whole documents or sections.
     starts with an identifier, which should not be modified), and
     ending with the apropriate punctuation.
 
+    These macros are only defined within the content of the
+    \env{seealso} environment.
+
     \begin{macrodesc}{seemodule}{\op{key}\p{name}\p{why}}
       Refer to another module.  \var{why} should be a brief
       explanation of why the reference may be interesting.  The module