Fixes small bug in struct proc_t documentation.

From http://man7.org/linux/man-pages/man5/proc.5.html:

(22) starttime  %llu
                        The time the process started after system boot.  In
                        kernels before Linux 2.6, this value was expressed
                        in jiffies.  Since Linux 2.6, the value is expressed
                        in clock ticks (divide by sysconf(_SC_CLK_TCK)).
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