add pydu.cmd.cmdline_argv() to cmd doc

docs/cmd.rst

@@ -14,3 +14,17 @@ Cmd
     (0, b'hello\r\n')  # Python 3
     >>> execute('echo hello', wait=False)
     <subprocess.Popen at 0x22e4010f9e8>
+
+
+.. function:: pydu.cmd.cmdline_argv()
+
+    Get command line argv of self python process. On Windows when using Python 2,
+    ``cmdline_argv`` is implemented by using ``shell32.GetCommandLineArgvW`` to get
+    sys.argv as a list of Unicode strings. On other system or using Python 3,
+    ``cmdline_argv`` is same to ``sys.argv``.
+
+    There is an example on PyCharm Python Console:
+
+    >>> from pydu.cmd import cmdline_argv
+    >>> cmdline_argv()
+    ['/Applications/PyCharm.app/Contents/helpers/pydev/pydevconsole.py', '61253', '61254']