Update datamode_code_generator:typo in pip install (#1713)

As seen in https://koxudaxi.github.io/datamodel-code-generator, the correct command is 
`pip install datamodel-code-generator`
not
`pip install datamodel-code-generato`

docs/datamodel_code_generator.md

@@ -8,7 +8,7 @@
 
 ## Install
 ```bash
-pip install datamodel-code-generato
+pip install datamodel-code-generator
 ```
 
 ## Example