align README.md and index.md

Submitter checklist

[x] Recommended: Join WireMock Slack to get any help in #help-contributing or a project-specific channel like #wiremock-java
[x] The PR request is well described and justified, including the body and the references
[x] The PR title represents the desired changelog entry
[x] The repository's code style is followed (see the contributing guide)
[x] 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