Here's how the formatting works: https://docs.github.com/en/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax

and here's the specific syntax for inserting a gif (just replace the svg link with your gif link):

![This is an image](https://myoctocat.com/assets/images/base-octocat.svg)