Add a todo

DEVELOPMENT.md

@@ -64,3 +64,10 @@ request anyway and we can work on getting it up to snuff.
   `$PROJECT_ROOT/.would-reformat/bin` instead.
 - `PROJECT_ROOT` and `WF_ROOT` are probably too generic.  Consider prefixing
   them, maybe with `WOULD_FORMAT_`.
+
+# To do
+
+- Some errors internal to `would-reformat` aren't properly signalled.  See
+  [RETURN-VALUES.md](RETURN-VALUES.md) for some.  Others still need to be
+  defined.
+

RETURN-VALUES.md

@@ -0,0 +1,5 @@
+To avoid confusion, we should probably stay away from numbers that are low and
+number that are near 255 as much as we can.
+
+101 - problem with pushd
+102 - problem with popd