Fix README.rst for pypi upload

[tomach]

Summary of the changes / Why this is an improvement

Pypi upload seems to fail when images have a scale factor. in this case twine reports:

$ twine check dist/*
Checking dist/croud-1.12.0-py2.py3-none-any.whl: FAILED
ERROR    `long_description` has syntax errors in markup and would not be rendered on PyPI.                                                                                                                          
         line 50: Warning: Cannot scale image!                                                                                                                                                                      
           Could not get size from "https://github.com/crate/croud/actions/workflows/docs.yml/badge.svg":                                                                                                           
           Requires Python Imaging Library.                                                                                                                                                                         
           Reading external files disabled.                                                                                                                                                                         
WARNING  `long_description_content_type` missing. defaulting to `text/x-rst`.                                                                                                                                       
Checking dist/croud-1.12.0.tar.gz: FAILED
ERROR    `long_description` has syntax errors in markup and would not be rendered on PyPI.                                                                                                                          
         line 50: Warning: Cannot scale image!                                                                                                                                                                      
           Could not get size from "https://github.com/crate/croud/actions/workflows/docs.yml/badge.svg":                                                                                                           
           Requires Python Imaging Library.                                                                                                                                                                         
           Reading external files disabled.                                                                                                                                                                         
WARNING  `long_description_content_type` missing. defaulting to `text/x-rst`.

Checklist

• Link to issue this PR refers to (if applicable):
• CLA is signed