add lab2

Labs/Lab2/git-conflict/README.md

Labs/Lab2/git-conflict/repo.zip

Labs/Lab2/git-pr/0.png

Labs/Lab2/git-pr/1.png

Labs/Lab2/git-pr/10.png

Labs/Lab2/git-pr/11.png

Labs/Lab2/git-pr/2.png

Labs/Lab2/git-pr/3.png

Labs/Lab2/git-pr/4.png

Labs/Lab2/git-pr/5.png

Labs/Lab2/git-pr/6.png

Labs/Lab2/git-pr/7.png

Labs/Lab2/git-pr/8.png

Labs/Lab2/git-pr/9.png

Labs/Lab2/git-pr/PR_list.png

Labs/Lab2/git-pr/README.md

Labs/Lab2/git-sim/1.png

Labs/Lab2/git-sim/2.png

Labs/Lab2/git-sim/README.md

Labs/Lab2/git-sim/solution.md