Improve git step documentation - #1744

Improve git step documentation

• Link to the documentation of the checkout step so that users of the git step can click the link for more information
• Better introduction sentence
• Use more modern branch name in example

Testing done

Confirmed that added hyperlinks are valid. Confirmed that the links work as expected and the page renders as expected.

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue