I know with that an image can be placed in a MD with the MD syntax of either ![Alt text](/path/to/img.jpg) or ![Alt text](/path/to/img.jpg "Optional
![Alt text](/path/to/img.jpg)
![Alt text](/path/to/img.jpg "Optional
I contacted GitHub to say that github.io-hosted SVGs are no longer displayed in GitHub READMEs. I received this reply:
We have had to disable svg image rendering on GitHub.com due to potential cross site scripting vulnerabilities.