docs: Remove old reference to update command (openapi-generators#1078)

Fixes openapi-generators#1075

Author: dbanty

README.md

@@ -49,10 +49,10 @@ You can use an OpenAPI file instead of a URL like `openapi-python-client generat
 
 ### Using custom templates
 
-This feature leverages Jinja2's [ChoiceLoader](https://jinja.palletsprojects.com/en/2.11.x/api/#jinja2.ChoiceLoader) and [FileSystemLoader](https://jinja.palletsprojects.com/en/2.11.x/api/#jinja2.FileSystemLoader). This means you do _not_ need to customize every template. Simply copy the template(s) you want to customize from [the default template directory](openapi_python_client/templates) to your own custom template directory (file names _must_ match exactly) and pass the template directory through the `custom-template-path` flag to the `generate` and `update` commands. For instance,
+This feature leverages Jinja2's [ChoiceLoader](https://jinja.palletsprojects.com/en/2.11.x/api/#jinja2.ChoiceLoader) and [FileSystemLoader](https://jinja.palletsprojects.com/en/2.11.x/api/#jinja2.FileSystemLoader). This means you do _not_ need to customize every template. Simply copy the template(s) you want to customize from [the default template directory](openapi_python_client/templates) to your own custom template directory (file names _must_ match exactly) and pass the template directory through the `custom-template-path` flag to the `generate` command:
 
 ```
-openapi-python-client update \
+openapi-python-client generate \
   --url https://my.api.com/openapi.json \
   --custom-template-path=relative/path/to/mytemplates
 ```