Fix README(Add python3.9).

Author: pyohei

README.md

@@ -1,4 +1,4 @@
-# Docker(Ubuntu18.04) for cgi with python(2.7/3.6/3.7/3.8)
+# Docker(Ubuntu18.04) for cgi with python(2.7/3.6/3.7/3.8/3.9)
 
 This is a simple python web server settings.  
 With this docker image, you can create simple web application with cgi.  
@@ -21,13 +21,15 @@ You can Access from the below URL after run docker container.
 * Python3.6 ... [http://localhost:8883/cgi-bin2/py36.cgi](http://localhost:8883/cgi-bin2/py36.cgi)
 * Python3.7 ... [http://localhost:8883/cgi-bin2/py37.cgi](http://localhost:8883/cgi-bin2/py37.cgi)
 * Python3.8 ... [http://localhost:8883/cgi-bin2/py38.cgi](http://localhost:8883/cgi-bin2/py38.cgi)
+* Python3.9 ... [http://localhost:8883/cgi-bin2/py39.cgi](http://localhost:8883/cgi-bin2/py39.cgi)
 
 ## Allow Python version
 
 * 2.7
 * 3.6
 * 3.7
 * 3.8
+* 3.9
 
 ### References