docs: put sleepy in the readme

Author: nedbat

README.rst

@@ -18,6 +18,8 @@ Code coverage measurement for Python.
 |  |tidelift| |sponsor| |stars| |mastodon-coveragepy| |mastodon-nedbat|
    |bluesky-nedbat|
 
+.. image:: https://coverage.readthedocs.io/en/7.8.1/_static/sleepy-snake-circle-150.png
+
 Coverage.py measures code coverage, typically during test execution. It uses
 the code analysis tools and tracing hooks provided in the Python standard
 library to determine which lines are executable, and which have been executed.