China (and a few other authoritarian countries) have blocked and attacked GitHub numerous times due to repos that are critical of the government or help bypass censorship (https://en.m.wikipedia.org/wiki/Censorship_of_GitHub).

But blocking GitHub has proven to be very costly so they're often forced to revert the decision. That's why GitHub appear to be the perfect place to host and promote truthful content (e.g. wiki articles about tiananmen massacre, xijiang concentration camps, etc) along with detailed instructions to bypass censorship. Right now it appear that at best China can prevent a specific URL from being shared on weixin/weibo/etc but can't stop people from opening the repo if they find a creative way to share it after (e.g. put the link in an image and modify the image slightly to change its hash before sharing it).