docs: update testpypi guide for api token

With the upcoming change to require 2FA for all users (already enforced
on TestPyPI), update guidance to point the user in the right direction.

Signed-off-by: Mike Fiedler <miketheman@gmail.com>

Author: miketheman

source/guides/using-testpypi.rst

@@ -72,12 +72,13 @@ you're testing has dependencies:
 Setting up TestPyPI in :file:`.pypirc`
 --------------------------------------
 
-If you want to avoid entering your username, you can configure TestPyPI in
-your :file:`$HOME/.pypirc`:
+If you want to avoid being prompted for your username and password every time,
+you can configure TestPyPI in your :file:`$HOME/.pypirc`:
 
 .. code:: ini
 
     [testpypi]
-    username = <your TestPyPI username>
+    username = __token__
+    password = <your TestPyPI API Token>
 
 For more details, see the :ref:`specification <pypirc>` for :file:`.pypirc`.