Description

Update README.md with absolute url for the header image

Checklist:

[x] I have read the CONTRIBUTING document.
[x] I have added tests that prove my fix is effective or that my feature works.
[x] I have run pre-commit locally prior to submission and fixed any errors/warnings.
[x] I have run tests locally prior to submission and they are passing.
[x] I have added necessary documentation (if appropriate).
[x] I have updated the README (if appropriate).
[x] I have updated the CHANGELOG (if appropriate).
[x] I have updated the version number (if appropriate).
[x] I have updated the requirements (if appropriate).