Clear set-up steps in Contributing.md file

Pull Request Description

Summary: [Provide a brief summary of the changes introduced by this pull request.]

Related Issue: [Specify the issue number or describe the problem that this pull request addresses.]

Description: [Provide a detailed description of the changes made in this pull request.]

Motivation and Context: [Explain the motivation behind these changes and the impact they have on the project.]

Please review and check the following items before submitting your pull request:

[ ] I have executed the command flutter pub run build_runner build to generate the necessary auto routes files.
[ ] I have verified that the auto route generation did not introduce any errors or warnings.
[ ] I have tested the changes locally and they are functioning as expected.
[ ] My code follows the project's coding style and guidelines.
[ ] All existing and new tests are passing.
[ ] I have added necessary documentation or updated existing documentation (if applicable).
[ ] I have added appropriate unit tests or updated existing tests (if applicable).
[ ] My commits are descriptive and follow the project's commit message conventions.
[ ] I have rebased my branch on the latest main branch.

Before: [Add screenshots or GIFs showing the state before the changes (if applicable).]

After: [Add screenshots or GIFs showing the state after the changes (if applicable).]