Fixed typo in docs/request_response.txt

    It's possible that a request can come in via POST with an empty ``POST``

    dictionary -- if, say, a form is requested via the POST HTTP method but

    does not include form data. Therefore, you shouldn't use ``if request.POST``

    to check for use of the POST method; instead, use ``if reuqest.method ==

    to check for use of the POST method; instead, use ``if request.method ==

    "POST"`` (see above).

    Note: ``POST`` does *not* include file-upload information. See ``FILES``.