Add Resource Controls to SystemD

Add some documentation around resource controls for SystemD

systemd/resource-control.service

+# Override file to specify CPU and RAM limits. Create a directory
+# /etc/systemd/system/<service-name>.service.d and place a file
+# with these contents inside with a .conf extension.
+
+[Service]
+# Assign the specified CPU time quota to the processes executed.
+# Takes a percentage value, suffixed with "%". The percentage
+# specifies how much CPU time the unit shall get at maximum,
+# relative to the total CPU time available on one CPU. Use
+# values > 100% for allotting CPU time on more than one CPU. This
+# controls the "cpu.max" attribute on the unified control group
+# hierarchy and "cpu.cfs_quota_us" on legacy. For details about
+# these control group attributes, see Control Groups v2 and
+# sched-bwc.txt.
+# Example: CPUQuota=20% ensures that the executed processes will
+# never get more than 20% CPU time on one CPU.
+CPUQuota=20%
+
+# Specify the throttling limit on memory usage of the executed
+# processes in this unit. Memory usage may go above the limit if
+# unavoidable, but the processes are heavily slowed down and memory
+# is taken away aggressively in such cases. This is the main
+# mechanism to control memory usage of a unit.
+# Takes a memory size in bytes. If the value is suffixed with
+# K, M, G or T, the specified memory size is parsed as Kilobytes,
+# Megabytes, Gigabytes, or Terabytes (with the base 1024),
+# respectively. Alternatively, a percentage value may be specified,
+# which is taken relative to the installed physical memory on the
+# system. If assigned the special value "infinity", no memory
+# throttling is applied. This controls the "memory.high" control
+# group attribute. For details about this control group attribute,
+# see Memory Interface Files.
+# This setting is supported only if the unified control group
+# hierarchy is used and disables MemoryLimit=.
+MemoryHigh=512M