Update README template to better align with drupal.org template

[gitressa]

The tool works great, and I just generated a module with it.

I did notice that there a few differences between the resulting README and the drupal.org README.md template, so perhaps we can make a few adjustments, to better align them?

This would also allow us to remove this tip on the README.md template page:

You can generate a boilerplate README.md with the following command: drush generate readme. The generated text does not follow these guidelines exactly, but may serve as a good starting point.

The PR makes these changes:

• Project name is the first line of the document, and only level one heading (#)
• Headings capitalized with an initial capital, following standard English sentence rules
• Two lines prior to ##/### headings
• Link module installation to current Drupal 11 page (was Drupal 7)