How are narrowly thematic Q&A services promoted?

Question

Computer networks

Hello! I asked myself such a question, how are narrow-topic Q&A services promoted?
Well, for example, the Toaster unwound like this: these were questions / answers on Habré, then it was transferred to a separate project. Accordingly, there was practically an audience, plus it is thematically useful.
And if you take for example any narrow topic, any at all. For example, a movie, a brand, or a community of gardeners/owners of watches of a certain brand/millers. How to let people know that there is such a service?
To score questions and answers yourself, and then wait for traffic from the PS?
After all, even if you try the context, then it is necessary, for example, to create an announcement for each question, because. hardly anyone enters in the search "Q&A printers".
Here is a question.

Answer 1

If I knew the buyback, I would become a millionaire

Answer 2

Option 1: major sponsor
2. word of mouth
3. hands. you write on different sites, leave your link to your site.
4. seo
5. and so you can combine all this into the flesh to infinity.
It goes without saying that this is a drop in the ocean!!