perlfunc: document return behavior of require

Author: Grinnz

pod/perlfunc.pod

@@ -7136,6 +7136,11 @@ affects the compilation unit within which the feature is used, and using
 it before requiring a module will not change the behavior of existing
 modules that do not themselves also use it.
 
+In this usage, the (truthy) result of the required file will be returned,
+but this should not be relied upon as it will not be returned in subsequent
+C<require> calls on the same file or with the 'module_true' feature enabled.
+To run a file and retrieve its return value, use L<C<do>|/do EXPR>.
+
 If EXPR is a bareword, C<require> assumes a F<.pm>
 extension and replaces C<::> with C</> in the filename for you,
 to make it easy to load standard modules.  This form of loading of