add code comment, fix layout (pdb_demo1.py)

Author: yennanliu

py_debugger/pdb_demo1.py

@@ -5,8 +5,17 @@
 import pdb
 
 def add(num1, num2):
-	pdb.set_trace()
-	return num1 + num2 
+    pdb.set_trace()
+    return num1 + num2 
 
 if __name__ == '__main__':
-	add(4, "abcvswfwe")
+    """
+    pdb useful command 
+    
+    help
+    a 
+    next
+    list
+    step
+    """
+    add(4, "abcvswfwe")