Fix fluid dist benchmark document errors (#8512)

Fix fluid dist benchmark document errors

Author: typhoonzero

benchmark/cluster/vgg16/README.md

@@ -8,10 +8,12 @@
 - cpu MHz		: 2101.000
 - cache size	: 20480 KB
 
+### Blas settings
+
+Setting environment variable: `MKL_NUM_THREADS=1`.
+
 ### Single Node Single Thread
 
-- PServer Count: 10
-- Trainer Count: 20
 - Metrics: samples / sec
 
 | Batch Size | 32 | 64 | 128 | 256 |
@@ -24,7 +26,6 @@
 
 - PServer Count: 10
 - Trainer Count: 20
-- Per trainer CPU Core: 1
 - Metrics: samples / sec
 
 | Batch Size | 32 | 64 | 128 | 256 |