tracing/fastboot: improve help text

	select TRACING

	help

	  This tracer helps developers to optimize boot times: it records

	  the timings of the initcalls. Its aim is to be parsed by the

	  /scripts/bootgraph.pl tool to produce pretty graphics about

	  boot inefficiencies, giving a visual representation of the

	  delays during initcalls. Note that tracers self tests can't

	  be enabled if this tracer is selected since only one tracer

	  should touch the tracing buffer at a time.

	  the timings of the initcalls and traces key events and the identity

	  of tasks that can cause boot delays, such as context-switches.

	  Its aim is to be parsed by the /scripts/bootgraph.pl tool to

	  produce pretty graphics about boot inefficiencies, giving a visual

	  representation of the delays during initcalls - but the raw

	  /debug/tracing/trace text output is readable too.

	  ( Note that tracing self tests can't be enabled if this tracer is

	    selected, because the self-tests are an initcall as well and that

	    would invalidate the boot trace. )

config STACK_TRACER

	bool "Trace max stack"