I feel like each community should have their own criteria and rules for how they want their members posts to be. Choosing an arbitrary number like 100 words doesn't make sense to me. Micromanaging and telling people how they should make their posts is not encouraging. Simply saying something like "I would love to know how u made this?" or any other question that revealed that you actually wanted to know more about the subject matter would suffice in encouraging people to provide more content in their posts. I agree with you on the fact that posts would be of better quality in general if there was more text, but the way you are going about it may push people away.

Not trying to argue, just wanted to share my opinion. Cheers.