Update README and step descriptions to be more informative

[dageforce]

Checklist

• I've read and followed the Contribution Guidelines
• step.yml and README.md is updated with the changes (if needed)

Version

Requires a PATCH version update

Context

Updates README.md and step documentation to fix minor issues, be more informative and match Appetize.io's current documentation links.

Changes

• Updated README.md to show additional info and match Appetize's other supporting templates.
• Updates step to fix some minor issues (e.g. numbering being incorrect) and update links to new documentation.

Investigation details

N/A

Decisions

• Intentionally added details in README with regards to host and API (from this PR) as we would like to see this included to support our Private cloud customers who have a custom domain name.

[lpusok]

Note: there is a way to autogenerate the readme:

  generate_readme:
    steps:
    - git::https://github.com/bitrise-steplib/steps-readme-generator.git: {}