perf kmem: Document a missing option & an argument

First, 'perf kmem' has a '--force' option, but didn't document it on the
man page. So add it.

Second, the '--time' option has to get a value, but isn't documented on
the man page. Describe it.

Signed-off-by: Sangwon Hong <qpakzk@gmail.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Taeung Song <treeze.taeung@gmail.com>
Link: http://lkml.kernel.org/r/1518381517-30766-1-git-send-email-qpakzk@gmail.com
[ Add blank like after --force block, as requested by Namhyung ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-kmem.txt

@@ -25,6 +25,10 @@ OPTIONS
 --input=<file>::
 	Select the input file (default: perf.data unless stdin is a fifo)
 
+-f::
+--force::
+	Don't do ownership validation
+
 -v::
 --verbose::
         Be more verbose. (show symbol address, etc)
@@ -61,7 +65,7 @@ OPTIONS
 	default, but this option shows live (currently allocated) pages
 	instead.  (This option works with --page option only)
 
---time::
+--time=<start>,<stop>::
 	Only analyze samples within given time window: <start>,<stop>. Times
 	have the format seconds.microseconds. If start is not given (i.e., time
 	string is ',x.y') then analysis starts at the beginning of the file. If