Docs: add more links to PIPE in subprocess docs (python#25416)

Doc/library/subprocess.rst

@@ -52,10 +52,12 @@ underlying :class:`Popen` interface can be used directly.
 
    If *capture_output* is true, stdout and stderr will be captured.
    When used, the internal :class:`Popen` object is automatically created with
-   ``stdout=PIPE`` and ``stderr=PIPE``. The *stdout* and *stderr* arguments may
-   not be supplied at the same time as *capture_output*.  If you wish to capture
-   and combine both streams into one, use ``stdout=PIPE`` and ``stderr=STDOUT``
-   instead of *capture_output*.
+   *stdout* and *stdin* both set to :data:`~subprocess.PIPE`.
+   The *stdout* and *stderr* arguments may not be supplied at the same time as *capture_output*.
+   If you wish to capture and combine both streams into one,
+   set *stdout* to :data:`~subprocess.PIPE`
+   and *stderr* to :data:`~subprocess.STDOUT`,
+   instead of using *capture_output*.
 
    A *timeout* may be specified in seconds, it is internally passed on to
    :meth:`Popen.communicate`. If the timeout expires, the child process will be
@@ -69,7 +71,8 @@ underlying :class:`Popen` interface can be used directly.
    subprocess's stdin.  If used it must be a byte sequence, or a string if
    *encoding* or *errors* is specified or *text* is true.  When
    used, the internal :class:`Popen` object is automatically created with
-   ``stdin=PIPE``, and the *stdin* argument may not be used as well.
+   *stdin* set to :data:`~subprocess.PIPE`,
+   and the *stdin* argument may not be used as well.
 
    If *check* is true, and the process exits with a non-zero exit code, a
    :exc:`CalledProcessError` exception will be raised. Attributes of that