Add documentation of the setup.cfg flag for pdb

doc/development.md

@@ -90,7 +90,7 @@ To run a single nose test:
     nosetests common/lib/xmodule/xmodule/tests/test_stringify.py:test_stringify
 
 
-Very handy: if you uncomment the `--pdb` argument in `NOSE_ARGS` in `lms/envs/test.py`, it will drop you into pdb on error.  This lets you go up and down the stack and see what the values of the variables are.  Check out http://docs.python.org/library/pdb.html
+Very handy: if you uncomment the `pdb=1` line in `setup.cfg`, it will drop you into pdb on error.  This lets you go up and down the stack and see what the values of the variables are.  Check out http://docs.python.org/library/pdb.html
 
 
 ### Javascript Tests