Add datamodel-code-generator link in pydantic document site (#1532)

* Add datamodel-code-generator link in pydantic document site.

* tweak menu

* fix blank lines

Co-authored-by: Samuel Colvin <samcolvin@gmail.com>
Co-authored-by: Samuel Colvin <s@muelcolvin.com>

changes/1500-koxudaxi.md

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+Add datamodel-code-generator link in pydantic document site.

docs/datamodel_code_generator.md

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+[datamodel-code-generator](https://github.com/koxudaxi/datamodel-code-generator/) is a command to generate pydantic models from other data types.
+
+
+* Supported source types
+    * OpenAPI 3 (YAML/JSON)
+    * JSON Schema
+    * JSON/YAML Data (It will be converted to JSON Schema)
+
+## Install
+```bash
+pip install datamodel-code-generato
+```
+
+## Example
+In this case, The datamodel-code-generator creates pydantic models from JSON Schema.
+```bash
+datamodel-codegen  --input person.json --input-file-type jsonschema --output model.py
+```
+
+person.json:
+```json
+{
+  "$id": "person.json",
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "title": "Person",
+  "type": "object",
+  "properties": {
+    "first_name": {
+      "type": "string",
+      "description": "The person's first name."
+    },
+    "last_name": {
+      "type": "string",
+      "description": "The person's last name."
+    },
+    "age": {
+      "description": "Age in years.",
+      "type": "integer",
+      "minimum": 0
+    },
+    "pets": {
+      "type": "array",
+      "items": [
+        {
+          "$ref": "#/definitions/Pet"
+        }
+      ]
+    },
+    "comment": {
+      "type": "null"
+    }
+  },
+  "required": [
+      "first_name",
+      "last_name"
+  ],
+  "definitions": {
+    "Pet": {
+      "properties": {
+        "name": {
+          "type": "string"
+        },
+        "age": {
+          "type": "integer"
+        }
+      }
+    }
+  }
+}
+```
+
+model.py:
+```py
+{!.tmp_examples/generate_models_person_model.py!}
+```
+
+More information can be found on the
+[official documentation](https://koxudaxi.github.io/datamodel-code-generator/)

docs/examples/generate_models_person_model.py

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+# generated by datamodel-codegen:
+#   filename:  person.json
+#   timestamp: 2020-05-19T15:07:31+00:00
+from __future__ import annotations
+from typing import Any, List, Optional
+from pydantic import BaseModel, Field, conint
+
+
+class Pet(BaseModel):
+    name: Optional[str] = None
+    age: Optional[int] = None
+
+
+class Person(BaseModel):
+    first_name: str = Field(..., description="The person's first name.")
+    last_name: str = Field(..., description="The person's last name.")
+    age: Optional[conint(ge=0)] = Field(None, description='Age in years.')
+    pets: Optional[List[Pet]] = None
+    comment: Optional[Any] = None

mkdocs.yml

@@ -46,6 +46,7 @@ nav:
 - benchmarks.md
 - 'Mypy plugin': mypy_plugin.md
 - 'PyCharm plugin': pycharm_plugin.md
+- 'Code Generation': datamodel_code_generator.md
 - changelog.md
 
 markdown_extensions: