Update README.md with new feature: PyMarkdownLinter (#29)

Author: hspaans

README.md

@@ -7,6 +7,7 @@ This repository contains following features:
 - [django-upgrade](./src/django-upgrade/README.md): Django-upgrade
 - [pyadr](./src/pyadr/README.md): Python ADR
 - [pytest](./src/pytest/README.md): Pytest
+- [pymarkdownlnt](./src/pymarkdownlnt/README.md): PyMarkdownLinter
 - [pyupgrade](./src/pyupgrade/README.md): Pyupgrade
 - [rstcheck](./src/rstcheck/README.md): rstcheck
 - [sshpass](./src/sshpass/README.md): SSH Pass for Ansible