perf annotate browser: Help for cycling thru hottest instructions with TAB/shift+TAB

perf annotate browser: Help for cycling thru hottest instructions with TAB/shift+TAB

The popup help accessed via 'h' wasn't mentioning about TAB and
shift-TAB, just about 'H', which goes to the hottest line, while the
former two are the hotkeys for actually cycling thru the hottest lines.

Reported-by: Flavio Bruno Leitner <fbl@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Taeung Song <treeze.taeung@gmail.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-5ppym6odizfj1ifa4t7neiku@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>