Add git lab intro document

This MR is to add introduction document and also try to work with local git and remote GitLab.

• 1. Clone project
• 2. Create local branch, add document and push those changes to GitLab
• 3. Test push local branch to remote main
• 4. Test push local main to remote main
• 5. Finish basic content of introduction document
• 6. push all changes to remote branch

After all, close the MR, execute the merger operation.