Staging: android: Add lowmemorykiller documentation.

The lowmemorykiller driver lets user-space specify a set of memory thresholds

where processes with a range of oom_adj values will get killed. Specify the

minimum oom_adj values in /sys/module/lowmemorykiller/parameters/adj and the

number of free pages in /sys/module/lowmemorykiller/parameters/minfree. Both

files take a comma separated list of numbers in ascending order.

For example, write "0,8" to /sys/module/lowmemorykiller/parameters/adj and

"1024,4096" to /sys/module/lowmemorykiller/parameters/minfree to kill processes

with a oom_adj value of 8 or higher when the free memory drops below 4096 pages

and kill processes with a oom_adj value of 0 or higher when the free memory

drops below 1024 pages.

The driver considers memory used for caches to be free, but if a large

percentage of the cached memory is locked this can be very inaccurate

and processes may not get killed until the normal oom killer is triggered.