Website RT Kernel Instructions

Hello, just a heads up: our lab historically hasn't been able to successfully build the RT kernel through the procedure on the website. When we follow it, we consistently encounter build errors on the kernel.

Instead, we use the Polymetis prerequisites page from steps 1 to 2. Then we use [this page](https://frankaemika.github.io/docs/installation_linux.html#setting-up-the-real-time-kernel) from "Compiling the kernel" and onward. For some reason going this route avoids the issues we run into when exclusively following the Polymetis procedure, I don't know why.

Just figured I would bring this to your guy's attention :)