Rename readme.md to README.md

[oleg-nenashev]

Git goes crazy in the history without a rename

References

• TODO

Submitter checklist

• [ ] Recommended: Join WireMock Slack to get any help in #help-contributing or a project-specific channel like #wiremock-java
• [ ] Recommended: If you participate in Hacktoberfest 2023, make sure you're signed up there and in the WireMock form
• [ ] The PR request is well described and justified, including the body and the references
• [ ] The PR title represents the desired changelog entry
• [ ] The repository's code style is followed (see the contributing guide)
• [ ] Test coverage that demonstrates that the change works as expected
• [ ] For new features, there's necessary documentation in this pull request or in a subsequent PR to wiremock.org