I've had this discussion before and the conclusion was:
Keep it as general as possible. Lemmy is still growing and small and a niche community looks often dead.
Once the community becomes too big it's easier to split the community into more specific communities.
For example: we have quite a few communities about learning a specific language and they all seem inactive, so we are keeping a general community up ([email protected]) but don't limit the content to anything specific. You can ask generally about languages, learning, or a specific language and you are more likely to get an answer from others than if you go to a language specific community.
Once it's too big it will be easy for an active group of people to move to, say, [email protected] or something.
So, in short: start with a general community :)