Add GitHub action in CI section

Signed-off-by: Laurent Cheylus <[email protected]>

Author: lcheylus

README.md

@@ -113,6 +113,7 @@
 - [Cirrus CI](https://cirrus-ci.org/features/) - [FreeBSD support](https://cirrus-ci.org/guide/supported-computing-services/), [OpenBSD support WIP](https://github.com/cirruslabs/cirrus-ci-docs/issues/311)
 - [Sourcehut](https://man.sr.ht/builds.sr.ht/compatibility.md#openbsd) - OpenBSD, FreeBSD and NetBSD support
 - GitLab ([HowTo](https://frankgroeneveld.nl/2016/04/06/using-gitlab-ci-multi-runner-on-openbsd/)), [sysutils/gitlab-runner](http://openbsd-archive.7691.n7.nabble.com/new-sysutils-gitlab-runner-td365939.html#a365948)
+- GitHub action [vmactions/openbsd-vm](https://github.com/vmactions/openbsd-vm)
 - Travis CI ([Running FreeBSD in Travis-CI](https://erouault.blogspot.com/2016/09/running-freebsd-in-travis-ci.html))
 - MinCI https://github.com/kristapsdz/minci