Document substr(Range) coerces endpoints to Int

Author: zoffixznet

doc/Type/Str.pod6

@@ -949,7 +949,8 @@ multi-match options like C<:g> are used).
     multi method substr(Str:D $s: Range $from-to  --> Str:D)
 
 Returns a substring of the original string, between the indices specified by
-C<$from-to>'s endpoints or from index C<$from> and of length C<$chars>.
+C<$from-to>'s endpoints (coerced to L<Int>) or from index C<$from> and of
+length C<$chars>.
 
 Both C<$from> and C<$chars> can be specified as L<Callable>, which will be
 invoked with the L<length|/routine/chars> of the original string and the