Update Readme.md with correct python code

Readme.md

@@ -10,11 +10,15 @@ Do a parallel map(func, tasks) with numProc processes
 ## How to use
 
 ```python
+import os
+from time import sleep
+from random import randint
+from pyParallelRunAndWrite import parallelRunAndWrite as prw
+
 def testFunc(arg):
     ret=str(arg)+str(os.getpid())
     sleep(randint(2,5))
     return ret
 
-def test():
-    parallelRunAndWrite(testFunc, range(5), "testplop",  numProc=2, errFileName="errors")
+prw.parallelRunAndWrite(testFunc, range(5), "testplop",  numProc=2, errFileName="errors")
 ```