[REQ] [Dart] instructions in generated README are problematic

Created by: nickmeinhold

Is your feature request related to a problem? Please describe.

I spoke to someone today who was having issues trying to use a generated client as the README instructions are a bit confusing and incorrectly use a mapping value.

The generated README includes instructions like this:

If this Dart package is published to Github, please include the following in pubspec.yaml

name: api_client
version: 0.0.1
description: OpenAPI API client
dependencies:
  api_client:
    git: https://github.com/username/api_client.git
      version: 'any'

Describe the solution you'd like

Get rid of the first 3 three lines and the last line and change the wording a little so the instructions are:

If this Dart package is published to Github, add the following dependency to your pubspec.yaml

dependencies:
  api_client:
    git: https://github.com/username/api_client.git