Suggestions

Hey @jni,

I just taught this tutorial and had some thoughts, but I didn't want to do a PR in case you complete disagree :stuck_out_tongue:

Firstly, I've decided I like it much better than the SWC version. It's much more succinct and has less side-tracks. It also focuses much more on branching and collaboration. Note, I taught a mini version because I only had 1.5 hours.

Suggestions:
- [ ] Replace all `git commit -a -m "message"` with:

```
git add mars.txt
git commit -m "message"
```

I know this is a common shortcut, but I think it's a bad habit, particularly for beginners. It leads to lots of accidental committing of things as the project gets more complicated.
- [ ] I also skipped the alias bit, because I think it should be a side-note/advanced feature, not part of a beginner tutorial.
- [ ] Finally, I did lots of graph pictures on the wall for the branching bit. Not sure if I have the patience to draw them electrically, but if I did, that would be my suggestion!

No file or test is named in the issue. Start by locating the tutorial source and its Git command examples, then review the alias section and branching material against the three suggestions. Done means the agreed tutorial edits are applied consistently and any proposed diagrams are either added or explicitly scoped out.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.