pwd: add pwd -P, -L to TODO

* TODO: Add to-do entry for -P and -L options of pwd.

TODO

@@ -36,6 +36,11 @@ printf:
   platforms where the native *printf(3) is deficient.
   Suggestion from Eric Blake.
 
+pwd:
+  Implement the options -P and -L in a POSIX-compatible way.
+  Note the instructions in the initial paragraph of this file
+  before starting.
+
 renice: POSIX utility, needs implementing.
   suggestion from Karl Berry (among others).
   Bob Proulx is working on this.