Add example: The surprising comma

Closes https://github.com/satwikkansal/wtfpython/issues/1

README.md

@@ -1481,6 +1481,38 @@ tuple()
 
 ---
 
+### The surprising comma
+
+Suggested by @MostAwesomeDude in [this](https://github.com/satwikkansal/wtfPython/issues/1) issue.
+
+**Output:**
+```py
+>>> def f(x, y,):
+...     print(x, y)
+...
+>>> def g(x=4, y=5,):
+...     print(x, y)
+...
+>>> def h(x, **kwargs,):
+  File "<stdin>", line 1
+    def h(x, **kwargs,):
+                     ^
+SyntaxError: invalid syntax
+>>> def h(*args,):
+  File "<stdin>", line 1
+    def h(*args,):
+                ^
+SyntaxError: invalid syntax
+```
+
+#### 💡 Explanation:
+
+- Trailing comma is not always legal in formal parameters list of a Python function.
+-  In Python, the argument list is defined partially with leading commas and partially with trailing commas. This conflict causes situations where a comma is trapped in the middle, and no rule accepts it.
+-  **Note:** The trailing comma problem is [fixed in Python 3.6](https://bugs.python.org/issue9232). The remarks in [this](https://bugs.python.org/issue9232#msg248399) post discuss in brief different usages of trailing commas in Python.
+
+---
+
 ### For what?
 
 Suggested by @MittalAshok in [this](https://github.com/satwikkansal/wtfpython/issues/23) issue.