ktap need CONFIG_KALLSYMS_ALL support

Otherwise cannot found address of ftrace_events
Note that currently implementation is hacking style, ktap will not depend
on CONFIG_KALLSYMS if ftrace_events is exported by kernel, patch already sent.

update it in doc/introduction.txt

Thanks Ilya Voronin pointed this.

Reported-by: Oded Gabbay <ogabbay@advaoptical.com>
Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@huawei.com>