Fix instructions in Lesson 12: Macros

The previous instructions don't work because the `cw` command leaves the cursor at the end of DONE, so the `j` command leaves it on the final character of TODO. The next `cw` command only changes this final character rather than the whole word. This adds a `^` command after the `j` to make it repeatable. It also clarifies the second step which says to "move back" even though the cursor should be on the second line already.