tracing/eprobe: Fix to add filter on eprobe description in README file

Fix to add a description of the filter on eprobe in README file. This
is required to identify the kernel supports the filter on eprobe or not.

Link: https://lore.kernel.org/all/167309833728.640500.12232259238201433587.stgit@devnote3/



Fixes: 752be5c5 ("tracing/eprobe: Add eprobe filter support")
Cc: stable@vger.kernel.org
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>