updated README.md

Tsung-Wei Huang · Tsung-Wei Huang · commit 1e62637ea227 · 2018-06-12T23:31:41.000-04:00
diff --git a/README.md b/README.md
@@ -243,7 +243,7 @@ By default, the group size is 1. Changing the group size can force intra-group t
 and inter-group tasks to run in parallel.
 Depending on applications, different group sizes can result in significant performance hit.
 
-<img align="right" height="40%" src="image/parallel_for_2.png">
+<img align="right" width="20%" src="image/parallel_for_2.png">
 
 ```cpp
 // apply callable to two container items at a time in parallel
