Update FrOST install script to install Linux Headers instead

[fe-wickham]

Instead of cloning the Linux repo in the getting started script, we could try installing the linux-headers package for our kernel version

https://www.tecmint.com/install-kernel-headers-in-ubuntu-and-debian/

If we can get that installed for 5.4.34-lts, I think that should be all we need to be able to build kernel modules

This might also be of interest: https://github.com/balena-os/module-headers
@tvannoy

[tvannoy]

We should be able to package up the kernel headers for whatever kernel version we are using make headers_install. Documentation here