perf time-utils: Fix --time documentation

Correct some punctuation and spelling and correct the format to show
that the time resolution is nanoseconds not microseconds.
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/20190604130017.31207-16-adrian.hunter@intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-diff.txt

@@ -142,9 +142,9 @@ OPTIONS
 	  perf diff --time 0%-10%,30%-40%
 
 	It also supports analyzing samples within a 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 stop time is not given (i.e, time
+	<start>,<stop>. Times have the format seconds.nanoseconds. If 'start'
+	is not given (i.e. time string is ',x.y') then analysis starts at
+	the beginning of the file. If stop time is not given (i.e. time
 	string is 'x.y,') then analysis goes to the end of the file. Time string is
 	'a1.b1,c1.d1:a2.b2,c2.d2'. Use ':' to separate timestamps for different
 	perf.data files.

tools/perf/Documentation/perf-report.txt

@@ -412,12 +412,12 @@ OPTIONS
 
 --time::
 	Only analyze samples within given time window: <start>,<stop>. Times
-	have the format seconds.microseconds. If start is not given (i.e., time
+	have the format seconds.nanoseconds. If start is not given (i.e. time
 	string is ',x.y') then analysis starts at the beginning of the file. If
-	stop time is not given (i.e, time string is 'x.y,') then analysis goes
+	stop time is not given (i.e. time string is 'x.y,') then analysis goes
 	to end of file.
 
-	Also support time percent with multiple time range. Time string is
+	Also support time percent with multiple time ranges. Time string is
 	'a%/n,b%/m,...' or 'a%-b%,c%-%d,...'.
 
 	For example:

tools/perf/Documentation/perf-script.txt

@@ -361,12 +361,12 @@ include::itrace.txt[]
 
 --time::
 	Only analyze samples within given time window: <start>,<stop>. Times
-	have the format seconds.microseconds. If start is not given (i.e., time
+	have the format seconds.nanoseconds. If start is not given (i.e. time
 	string is ',x.y') then analysis starts at the beginning of the file. If
-	stop time is not given (i.e, time string is 'x.y,') then analysis goes
+	stop time is not given (i.e. time string is 'x.y,') then analysis goes
 	to end of file.
 
-	Also support time percent with multipe time range. Time string is
+	Also support time percent with multiple time ranges. Time string is
 	'a%/n,b%/m,...' or 'a%-b%,c%-%d,...'.
 
 	For example: