add simple doc of whl

ppstructure/README_ch.md

 # TableStructurer
+
+1. 代码使用
+```python
+import cv2
+from paddlestructure import PaddleStructure,draw_result
+
+table_engine = PaddleStructure(
+    output='./output/table',
+    show_log=True)
+
+img_path = '../doc/table/1.png'
+img = cv2.imread(img_path)
+result = table_engine(img)
+for line in result:
+    print(line)
+
+from PIL import Image
+
+font_path = 'path/tp/PaddleOCR/doc/fonts/simfang.ttf'
+image = Image.open(img_path).convert('RGB')
+im_show = draw_result(image, result,font_path=font_path)
+im_show = Image.fromarray(im_show)
+im_show.save('result.jpg')
+```
+
+2. 命令行使用
+```bash
+paddlestructure --image_dir=../doc/table/1.png
+```