missing link - Update Str.rakudoc

`syntax/s///` works but `/language/operators#s///_in-place_substitution` has more information

Author: finanalyst

doc/Type/Str.rakudoc

@@ -897,7 +897,7 @@ The C<:nth> adverb has readable English-looking variants:
 B<NOTE:> I<<< C<.subst-mutate> is deprecated in the 6.d version, and will be
 removed in future ones. You can use L<subst|/routine/subst> with L«C<.=> method
 call assignment operator|/routine/.=» or L«C<s///> substitution
-operator|/syntax/s$SOLIDUS$SOLIDUS$SOLIDUS» instead. >>>
+operator|/language/operators#s///_in-place_substitution» instead. >>>
 
 Where L<subst|/routine/subst> returns the modified string and leaves the
 original unchanged, it is possible to mutate the original string by using