tracing: rephrase for clearer documentation

Signed-off-by: Ryan Chung <[e-mail]>
Acked-by: Steven Rostedt (Google) <[e-mail]>
Signed-off-by: Jonathan Corbet <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

Documentation/trace/boottime-trace.rst

···
 Options in the Boot Config
 ==========================
 
-Here is the list of available options list for boot time tracing in
+Here is the list of available options for boot time tracing in
 boot config file [1]_. All options are under "ftrace." or "kernel."
 prefix. See kernel parameters for the options which starts
 with "kernel." prefix [2]_.