It's kind of promotion but this service is provided as a free one, not for commercial purpose. If this is against the spam policy, I'll delete my post.
That doesn't matter. Common courtesy dictates that you contact the site owner or an admin before promoting a website or a service. On top of that you did not disclose your professional relationship to the company providing that service. You just stated that you had "found a free online chatting service". That's dishonest and spam by definition.