Use site.github.url jekyll macro
Use site.github.url jekyll macro

This should allow the same repo content to host from
tianocore.github.io and $username.github.io/tianocore.

Signed-off-by: Jordan Justen <ab3d56373f2461770fa8feb620844a5acfe35e29@gmail.com>

jljusten/tianocore,Teino1978-Corp/Teino1978-Corp-tianocore.dashboard,Teino1978-Corp/Teino1978-Corp-tianocore.github.io,tianocore/tianocore.github.io,Teino1978-Corp/Teino1978-Corp-tianocore.dashboard,jljusten/tianocore,tianocore/tianocore.github.io,Teino1978-Corp/Teino1978-Corp-tianocore.github.io