docs: Add test badge to README

[Ic3w0lf]

What it solves

Add test badge to readme

Readiness Checklist

Author/Contributor

• If documentation is needed for this change, has that been included in this pull request
• Pull request title is brief and descriptive (for a changelog entry)

Reviewing Maintainer

• Label as breaking if this is a large fundamental change
• Label as either automation, bug, documentation, or enhancement
• Label as bump:patch, bump:minor, or bump:major if this PR should create a new release

[github-actions]

We require pull request titles to follow the Conventional Commits specification and it looks like your proposed title needs to be adjusted.

Details:

No release type found in pull request title "Add test badge to README". Add a prefix to indicate what kind of release this pull request corresponds to. For reference, see https://www.conventionalcommits.org/

Available types:
 - feat: A new feature
 - fix: A bug fix
 - docs: Documentation only changes
 - style: Changes that do not affect the meaning of the code (white-space, formatting, missing semi-colons, etc)
 - refactor: A code change that neither fixes a bug nor adds a feature
 - perf: A code change that improves performance
 - test: Adding missing tests or correcting existing tests
 - build: Changes that affect the build system or external dependencies (example scopes: gulp, broccoli, npm)
 - ci: Changes to our CI configuration files and scripts (example scopes: Travis, Circle, BrowserStack, SauceLabs)
 - chore: Other changes that don't modify src or test files
 - revert: Reverts a previous commit