[PATCH] Missing comma in usr_10.txt

```
"In chapter 4 several ways to make small changes were explained." - missing 
comma after "4". Patch attached.
```

Original issue reported on code.google.com by `shlomif@gmail.com` on 25 Jun 2011 at 6:47

Attachments:
- [vim.diff](https://storage.googleapis.com/google-code-attachments/vim/issue-16/comment-0/vim.diff)
