docs: update walkthrough and welcome

[Hellebore]

Checklist

• [ ] If package.json or yarn.lock have changed, then test the VSIX built by yarn run vsce package works from a direct install

Summary by Sourcery

This pull request updates the user-facing documentation in 'welcome-to-sourcery.py' to enhance the walkthrough and welcome instructions, making them more comprehensive and user-friendly.

• Documentation:
  • Updated the walkthrough in 'welcome-to-sourcery.py' to provide clearer instructions on using the coding assistant and the review tab, including details on code review functionality and Git version control requirements.

[sourcery-ai[bot]]

Reviewer's Guide by Sourcery

This pull request updates the 'welcome-to-sourcery.py' file to improve the walkthrough and welcome instructions. The changes focus on clarifying the usage of the coding assistant and the review tab, as well as reordering the instructions for better flow.

File-Level Changes

Files	Changes
welcome-to-sourcery.py	Improved the walkthrough and welcome instructions by updating the coding assistant introduction, adding 'Review' tab instructions, and reordering the content for better clarity.