Document .subst-mutate returns a List when :g is used

Author: zoffixznet

doc/Type/Str.pod6

@@ -721,8 +721,10 @@ regex, not the C<subst> method call.
 
 Where C<subst> returns the modified string and leaves the original
 unchanged, it is possible to mutate the original string by using
-C<subst-mutate>.  If the match is successful, the method returns a C<Match>
-object representing the successful match, or C<Any> otherwise.
+C<subst-mutate>. If the match is successful, the method returns a C<Match>
+object representing the successful match; if C<:g> (or C<:global>) argument
+is used, returns a C<List> of C<Match> objects. If no matches happen,
+returns C<Any>.
 
     my $some-string = "Some foo";
     my $match = $some-string.subst-mutate(/foo/, "string");