RFE: document the reasons that lvm2 commands need their own process

[DemiMarie]

Until recently, I was not able to find a clear explanation for why the lvm2 commands need a process to themselves. Only today did I finally understand that if an lvm2 command exits or is killed at the wrong point, it can leave the entire system frozen until reboot. That is certainly a legitimate reason for lvm2 to not be a library: another thread in the process could cause the process to exit (due to SIGSEGV, failed assertion, uncaught exception, etc) and bring the system down. This is a request that the matter be better documented, so that others are not as confused as I was.