Update subprocess.Popen documentation wrt universal_newlines arg (GH-10337)

* universal_newlines defaulting to False would suggest, that not
  specifying universal_newlines explicitly and setting text to True
  should cause an error, which is not the case.
* The run function didn't have the universal_newlines parameter
  documented
* The check_output function didn't have its text parameter documented

Doc/library/subprocess.rst

@@ -39,7 +39,8 @@ compatibility with older versions, see the :ref:`call-function-trio` section.
 
 .. function:: run(args, *, stdin=None, input=None, stdout=None, stderr=None,\
                   capture_output=False, shell=False, cwd=None, timeout=None, \
-                  check=False, encoding=None, errors=None, text=None, env=None)
+                  check=False, encoding=None, errors=None, text=None, env=None, \
+                  universal_newlines=None)
 
    Run the command described by *args*.  Wait for command to complete, then
    return a :class:`CompletedProcess` instance.
@@ -334,7 +335,7 @@ functions.
 
 .. class:: Popen(args, bufsize=-1, executable=None, stdin=None, stdout=None, \
                  stderr=None, preexec_fn=None, close_fds=True, shell=False, \
-                 cwd=None, env=None, universal_newlines=False, \
+                 cwd=None, env=None, universal_newlines=None, \
                  startupinfo=None, creationflags=0, restore_signals=True, \
                  start_new_session=False, pass_fds=(), *, \
                  encoding=None, errors=None, text=None)
@@ -1055,7 +1056,7 @@ calls these functions.
 
 .. function:: check_output(args, *, stdin=None, stderr=None, shell=False, \
                            cwd=None, encoding=None, errors=None, \
-                           universal_newlines=False, timeout=None)
+                           universal_newlines=None, timeout=None, text=None)
 
    Run command with arguments and return its output.
 
@@ -1101,6 +1102,10 @@ calls these functions.
    .. versionchanged:: 3.6
       *encoding* and *errors* were added.  See :func:`run` for details.
 
+   .. versionadded:: 3.7
+      *text* was added as a more readable alias for *universal_newlines*.
+
+
 .. _subprocess-replacements:
 
 Replacing Older Functions with the :mod:`subprocess` Module