Add section on disabling keyring. (#396)

README.rst

@@ -134,6 +134,15 @@ The next time you run ``twine`` it will prompt you for a username and will grab
 .. _`Using Keyring on headless systems`:
     https://keyring.readthedocs.io/en/latest/#using-keyring-on-headless-linux-systems
 
+Disabling Keyring
+^^^^^^^^^^^^^^^^^
+
+In some cases, the presence of keyring may be problemmatic. To disable
+keyring and defer to a prompt for passwords, uninstall ``keyring``
+or if that's not an option, you can also configure keyring to be disabled.
+
+See `twine 338 <https://github.com/pypa/twine/issues/338>`_ for a
+discussion on ways to do that.
 
 Options
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