add github actions bot with a hint comment for contributors.

[fsb4000]

Not for a merge but for demonstration for ovs-discuss@openvswitch.org

I thought about how best to reuse 0day robot checks, and I came up with the idea that it’s better not to create a pipeline with the checks, but it’s better to just tell contributors about how to submit a patch, what code style is used, and about 0day robot checks.

[fsb4000]

Strange, the bot message works locally: fsb4000/test#1

but here I got:

{
  "message": "Resource not accessible by integration",
  "documentation_url": "https://docs.github.com/rest/reference/issues#create-an-issue-comment"
}

[fsb4000]

I found the article: https://github.blog/2020-08-03-github-actions-improvements-for-fork-and-pull-request-workflows/

It will not work at PR before merging: fsb4000/test#2

But I hope it will work after: fsb4000/test#3

[fsb4000]

An example of an other project bot message: apache/airflow#25083 (comment)

[fsb4000]

it seems that we have openstack-mirroring bot: openstack/neutron#57 (comment)