You cannot import PDF as Readme, but I also don’t see the point as it support the wonderful MD Language which can be seen easily with any device (also mobile).
I have fixed the equations problem by using images. There is a nice website for that: http://mathurl.com/
Just type your latex equation and click “Make Math url” (bottom left button), the copy paste the image link (in red).
I have used it in the wiki of github (but it should work the same with readme.md): https://github.com/scholi/pySPM/wiki/Mass-calibration
Enjoy!