Bug #1739115: make shutil.rmtree docs clear wrt. file deletion.

Doc/lib/libshutil.tex

@@ -91,11 +91,12 @@ file type and creator codes will not be correct.
 \end{funcdesc}
 
 \begin{funcdesc}{rmtree}{path\optional{, ignore_errors\optional{, onerror}}}
-  Delete an entire directory tree.\index{directory!deleting}
-  If \var{ignore_errors} is true,
-  errors resulting from failed removals will be ignored; if false or
-  omitted, such errors are handled by calling a handler specified by
-  \var{onerror} or, if that is omitted, they raise an exception.
+  \index{directory!deleting}
+  Delete an entire directory tree (\var{path} must point to a directory).
+  If \var{ignore_errors} is true, errors resulting from failed removals
+  will be ignored; if false or omitted, such errors are handled by
+  calling a handler specified by \var{onerror} or, if that is omitted,
+  they raise an exception.
 
   If \var{onerror} is provided, it must be a callable that accepts
   three parameters: \var{function}, \var{path}, and \var{excinfo}.