Add a "Enable the nohz_full" hint when trying to apply the "scx_tickless(Server)" scxed-ext scheduler.

Seemed that "scx_tickless" need to work with nohz_full which needed to be configured in kernel. Add a hint in scx_manager when trying to enable "scx_tickless" in a kernel which didn't configure "nohz_full" may help the "scx_tickless" scheduler run correctly.

Related logs:
https://paste.cachyos.org/p/535645d.txt