fio:modify a deprecated parameter(change timeout to runtime)

since "timeout" had been deprecated long long ago, we should replace
to "runtime" both in code and docs

Signed-off-by: Liang Xie <xieliang@xiaomi.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/README b/README
index 8514c73..c629e2d 100644
--- a/README
+++ b/README
@@ -121,7 +121,7 @@
 $ fio
 	--debug			Enable some debugging options (see below)
 	--output		Write output to file
-	--timeout		Runtime in seconds
+	--runtime		Runtime in seconds
 	--latency-log		Generate per-job latency logs
 	--bandwidth-log		Generate per-job bandwidth logs
 	--minimal		Minimal (terse) output