Add docstring for shlex.split (GH-16740)

diff --git a/Lib/shlex.py b/Lib/shlex.py
index ae0f5dd..c817274 100644
--- a/Lib/shlex.py
+++ b/Lib/shlex.py
@@ -303,6 +303,7 @@
         return token
 
 def split(s, comments=False, posix=True):
+    """Split the string *s* using shell-like syntax."""
     lex = shlex(s, posix=posix)
     lex.whitespace_split = True
     if not comments: