Add "Spell Check" workflow badge to readme

The badges provide a prominent indication of the repository's CI status at a glance. This may help to bring potential
issues to the attention of the maintainers.

Author: per1234

README.md

@@ -8,6 +8,7 @@
 [![Publish Nightly Build status](https://github.com/arduino/arduino-lint/actions/workflows/publish-go-nightly-task.yml/badge.svg)](https://github.com/arduino/arduino-lint/actions/workflows/publish-go-nightly-task.yml)
 [![Check Python status](https://github.com/arduino/arduino-lint/actions/workflows/check-python-task.yml/badge.svg)](https://github.com/arduino/arduino-lint/actions/workflows/check-python-task.yml)
 [![Check Markdown status](https://github.com/arduino/arduino-lint/actions/workflows/check-markdown-task.yml/badge.svg)](https://github.com/arduino/arduino-lint/actions/workflows/check-markdown-task.yml)
+[![Spell Check status](https://github.com/arduino/arduino-lint/actions/workflows/spell-check-task.yml/badge.svg)](https://github.com/arduino/arduino-lint/actions/workflows/spell-check-task.yml)
 [![Check Website status](https://github.com/arduino/arduino-lint/actions/workflows/check-mkdocs-task.yml/badge.svg)](https://github.com/arduino/arduino-lint/actions/workflows/check-mkdocs-task.yml)
 [![Deploy Website status](https://github.com/arduino/arduino-lint/actions/workflows/deploy-cobra-mkdocs-versioned-poetry.yml/badge.svg)](https://github.com/arduino/arduino-lint/actions/workflows/deploy-cobra-mkdocs-versioned-poetry.yml)
 [![Codecov](https://codecov.io/gh/arduino/arduino-lint/branch/main/graph/badge.svg?token=nprqPQMbdh)](https://codecov.io/gh/arduino/arduino-lint)