Use Python 3.9 in README

Author: ymyzk

README.md

@@ -20,26 +20,28 @@ When running tox on GitHub Actions, tox-gh-actions
 
 ## Examples
 ### Basic Example
-The following configuration will create 4 jobs when running the workflow on GitHub Actions.
+The following configuration will create 5 jobs when running the workflow on GitHub Actions.
 - On Python 2.7 job, tox runs `py27` environment
 - On Python 3.6 job, tox runs `py36` environment
 - On Python 3.7 job, tox runs `py37` environment
 - On Python 3.8 job, tox runs `py38` and `mypy` environments
+- On Python 3.9 job, tox runs `py39` environment
 
 #### tox-gh-actions Configuration
 Add `[gh-actions]` section to the same file as tox's cofiguration.
 
 If you're using `tox.ini`:
 ```ini
 [tox]
-envlist = py27, py36, py37, py38, mypy
+envlist = py27, py36, py37, py38, py39, mypy
 
 [gh-actions]
 python =
     2.7: py27
     3.6: py36
     3.7: py37
     3.8: py38, mypy
+    3.9: py39
 
 [testenv]
 ...
@@ -48,14 +50,15 @@ python =
 If you're using `setup.cfg`:
 ```ini
 [tox:tox]
-envlist = py27, py36, py37, py38, mypy
+envlist = py27, py36, py37, py38, py39, mypy
 
 [gh-actions]
 python =
     2.7: py27
     3.6: py36
     3.7: py37
     3.8: py38, mypy
+    3.9: py39
 
 [testenv]
 ...
@@ -66,14 +69,15 @@ If you're using `pyproject.toml`:
 [tool.tox]
 legacy_tox_ini = """
 [tox]
-envlist = py27, py36, py37, py38, mypy
+envlist = py27, py36, py37, py38, py39, mypy
 
 [gh-actions]
 python =
     2.7: py27
     3.6: py36
     3.7: py37
     3.8: py38, mypy
+    3.9: py39
 
 [testenv]
 """
@@ -90,9 +94,9 @@ jobs:
   build:
     runs-on: ubuntu-latest
     strategy:
-      max-parallel: 4
+      max-parallel: 5
       matrix:
-        python-version: [2.7, 3.6, 3.7, 3.8]
+        python-version: [2.7, 3.6, 3.7, 3.8, 3.9]
 
     steps:
     - uses: actions/checkout@v1