bpo-37014: Update docstring and Documentation of fileinput.FileInput(). (GH-13545)

* bpo-37014: Update docstring and Documentation of fileinput.FileInput()

* Explain the behavior of fileinput.FileInput() when reading stdin.

* Update blurb.

* bpo-37014: Fix typo in the docstring and documentation.
diff --git a/Doc/library/fileinput.rst b/Doc/library/fileinput.rst
index 14be492..f5e5280 100644
--- a/Doc/library/fileinput.rst
+++ b/Doc/library/fileinput.rst
@@ -23,8 +23,9 @@
 
 This iterates over the lines of all files listed in ``sys.argv[1:]``, defaulting
 to ``sys.stdin`` if the list is empty.  If a filename is ``'-'``, it is also
-replaced by ``sys.stdin``.  To specify an alternative list of filenames, pass it
-as the first argument to :func:`.input`.  A single file name is also allowed.
+replaced by ``sys.stdin`` and the optional arguments *mode* and *openhook*
+are ignored.  To specify an alternative list of filenames, pass it as the
+first argument to :func:`.input`.  A single file name is also allowed.
 
 All files are opened in text mode by default, but you can override this by
 specifying the *mode* parameter in the call to :func:`.input` or