Update README.md

README.md

 # CVAT Annotation Rule
 
-* Annotate **upper half person**.
-* As tight as possible
-* Bounding box
-    - Bottom edge touches the belt/hip:
+## Annotation Target
+
+Only annotate the upper half of the body.
+
+## Annotation Rule
+
+* Annotate **upper half of the person**, as tight as possible
+* Bounding box rule
+  * Bottom edge touches the straight belt/hip:
   
       ![Straight belt](http://192.168.0.101:8929/nvmnghia/cvat-annotation-rule/raw/master/straight%20belt.png)
 
-    - Bottom edge touches the top point of the belt/hip
+  * Bottom edge touches the top point of the oblique belt/hip
 
       ![Oblique belt](http://192.168.0.101:8929/nvmnghia/cvat-annotation-rule/raw/c409536b319bff3e6c7bf69fc20404669cf85d84/oblique%20belt.png)
+
+  * Height must be more than 1/8 of the frame's height
+
+* Visibility rule
+  * Head must be visible
+  * The visible part of the upper half must be larger than 50% of the whole upper part
+  * The person must not be too small