docs: add note for supported Python versions (#174)

Author: mxschmitt

README.md

@@ -1,6 +1,6 @@
 # 🎭 [Playwright](https://github.com/microsoft/playwright) for Python
 
-[![PyPI version](https://badge.fury.io/py/playwright.svg)](https://pypi.python.org/pypi/playwright/) [![Join Slack](https://img.shields.io/badge/join-slack-infomational)](https://join.slack.com/t/playwright/shared_invite/enQtOTEyMTUxMzgxMjIwLThjMDUxZmIyNTRiMTJjNjIyMzdmZDA3MTQxZWUwZTFjZjQwNGYxZGM5MzRmNzZlMWI5ZWUyOTkzMjE5Njg1NDg) <!-- GEN:chromium-version-badge -->[![Chromium version](https://img.shields.io/badge/chromium-86.0.4217.0-blue.svg?logo=google-chrome)](https://www.chromium.org/Home)<!-- GEN:stop --> <!-- GEN:firefox-version-badge -->[![Firefox version](https://img.shields.io/badge/firefox-79.0a1-blue.svg?logo=mozilla-firefox)](https://www.mozilla.org/en-US/firefox/new/)<!-- GEN:stop --> [![WebKit version](https://img.shields.io/badge/webkit-14.0-blue.svg?logo=safari)](https://webkit.org/)
+[![PyPI version](https://badge.fury.io/py/playwright.svg)](https://pypi.python.org/pypi/playwright/) [![PyPI pyversions](https://img.shields.io/pypi/pyversions/playwright.svg)](https://pypi.python.org/pypi/playwright/) [![Join Slack](https://img.shields.io/badge/join-slack-infomational)](https://join.slack.com/t/playwright/shared_invite/enQtOTEyMTUxMzgxMjIwLThjMDUxZmIyNTRiMTJjNjIyMzdmZDA3MTQxZWUwZTFjZjQwNGYxZGM5MzRmNzZlMWI5ZWUyOTkzMjE5Njg1NDg) <!-- GEN:chromium-version-badge -->[![Chromium version](https://img.shields.io/badge/chromium-86.0.4217.0-blue.svg?logo=google-chrome)](https://www.chromium.org/Home)<!-- GEN:stop --> <!-- GEN:firefox-version-badge -->[![Firefox version](https://img.shields.io/badge/firefox-79.0a1-blue.svg?logo=mozilla-firefox)](https://www.mozilla.org/en-US/firefox/new/)<!-- GEN:stop --> [![WebKit version](https://img.shields.io/badge/webkit-14.0-blue.svg?logo=safari)](https://webkit.org/)
 
 ##### [Docs](#documentation) | [API reference](https://playwright.dev/#?path=docs/api.md) | [Docstrings](https://github.com/microsoft/playwright-python/blob/master/playwright/sync_api.py)
 
@@ -21,7 +21,7 @@ pip install playwright
 python -m playwright install
 ```
 
-This installs Playwright and browser binaries for Chromium, Firefox and WebKit. Once installed, you can `import` Playwright in a Python script and automate web browser interactions.
+This installs Playwright and browser binaries for Chromium, Firefox and WebKit. Once installed, you can `import` Playwright in a Python script and automate web browser interactions. Playwright requires Python 3.7+.
 
 ## Capabilities