perf report: Add mem-mode documentation to report command

	By default, every sort keys not specified in -F will be appended

	automatically.

	If --mem-mode option is used, following sort keys are also available

	(incompatible with --branch-stack):

	symbol_daddr, dso_daddr, locked, tlb, mem, snoop.

	- symbol_daddr: name of data symbol being executed on at the time of sample

	- dso_daddr: name of library or module containing the data being executed

	on at the time of sample

	- locked: whether the bus was locked at the time of sample

	- tlb: type of tlb access for the data at the time of sample

	- mem: type of memory access for the data at the time of sample

	- snoop: type of snoop (if any) for the data at the time of sample

	And default sort keys are changed to local_weight, mem, sym, dso,

	symbol_daddr, dso_daddr, snoop, tlb, locked, see '--mem-mode'.

-p::

--parent=<regex>::

        A regex filter to identify parent. The parent is a caller of this

	Demangle symbol names to human readable form. It's enabled by default,

	disable with --no-demangle.

--mem-mode::

	Use the data addresses of samples in addition to instruction addresses

	to build the histograms.  To generate meaningful output, the perf.data

	file must have been obtained using perf record -d -W and using a

	special event -e cpu/mem-loads/ or -e cpu/mem-stores/. See

	'perf mem' for simpler access.

--percent-limit::

	Do not show entries which have an overhead under that percent.

	(Default: 0).