[docs] optparse 'help' action is not documented

[anatoly techtonik]

Hi,

Documentation misses 'help' action for optparse, which is used
in `pip` and I suppose in other projects:
https://github.com/pypa/pip/blob/develop/pip/cmdoptions.py#L65

It will be more convenient for reference if instead of textual
description, the docs contained this table:

https://hg.python.org/cpython/file/2.7/Lib/optparse.py#l481

    # The set of actions allowed by option parsers.  Explicitly listed
    # here so the constructor can validate its arguments.
    ACTIONS = ("store",
               "store_const",
               "store_true",
               "store_false",
               "append",
               "append_const",
               "count",
               "callback",
               "help",
               "version")

-- 
anatoly t.