There was a question on Discord about why using Difftastic wasn't working as the
diff tool. The root cause was putting `ui.diff.tool` in the wrong toml section,
when the `ui.` component actually refers to the `[ui]` section itself.
This reads kind of weirdly too because _immediately_ after this, the alternative
option of using the `merge-tools` section is suggested; except it uses `[merge-
tools.<name>]` which makes it immediately clear it's a section on its own.
This simply these two examples more consistent with each other, by using `[ui]`
instead of `ui.` to make it clear `ui.` is a top-level section.
Signed-off-by: Austin Seipp <aseipp@pobox.com>
415ae5c0f9