As you might already know the version of Markdown that GitHub uses does not support adding videos. Although you might find work arounds if you search hard enough, the closest you'll get to is embedding a YouTube video in your markdown file. But what if you have a custom video? A video on your device?
Well, there's a workaround, it won't enable you to upload the video but you'll get the same results. The thing is GitHub READMEs work perfectly with GIFs. GIF is a bitmap graphical image format. So what you get isn't necessarily a video but the result is relatively similar.
Now all you have to do is obtain the desired video and use a tool such as CloudConvert to convert the video to a gif.
However, it's worth noting that the longer the video the bigger the size and you might experience some lagging depending on the type of video and the converting software used. Besides this you should generally get good results.
After converting the video to a GIF. All you have to do is create a GitHub repository with the same name as your GitHub username. For example my GitHub username is
mojpm so the new repository would also be called
Then simply add the GIF in your README.md file the same way you would add an image
![caption](link to image / GIF)
And that's all. Push your files to your GitHub account and you should have an impressive README.
You can checkout mine to see what I chose.