add write package

docs/en-US/guide/write-package.md

@@ -4,9 +4,49 @@
 
 ### Project Structure
 
+Your package is firstly a Python Package. Therefore, it will look like:
+
+```
+- example_package
+    - example_package
+        - solver.py
+        - bundle.py
+    - pretrained
+        - pretrained.toml
+    - tests // optional
+    - examples // optional
+    - cvpm.toml
+    - requirements.txt
+    - README.md
+```
+
 ### Solvers
 
+Solver is a ```class``` extended from ```cvpm.Solver``` class. In this class, you need to implement 2 functions: ```__init__``` and ```infer```. As their literal meanings, in the ```init``` function, parameters that your infer functions use should be initiate, and in the ```infer``` function, a image file path will be passed in the parameter, and the ```infer``` function is supposed to return your result in a dict or list.
+
+For example, a simple solver frame will look like 
+
+``` python
+from cvpm.solver import Solver
+
+class SampleSolver(Solver):
+    def __init__(self, toml_file=None):
+        super().__init__(toml_file)
+        # Do you Init Work here
+        self.classifer = get_classifier()
+        self.set_ready()
+    def infer(self, image_file, config):
+        # Use your own load_image method, or from cvpm.utility import load_image_file
+        image = load_image(image_file) 
+        result = self.classifier(image)
+        return result
+``` 
+
 ### Bundle
+
+::: tip 注意 请确保你的 Node.js 版本 >= 8。 :::
+
+
 
 ### cvpm.toml
 
@@ -27,4 +67,5 @@ Your README file should be look like
 ```
 
 You can look at [Face Utility](https://github.com/cvmodel/Face_Utility) for reference that we provided as an official repository.
+
 ## Best Practice