doc: clarify that --word-diff operates on line-level hunks #28035

Job	Run time
config	9s
fuzz smoke test	1m 8s
win build	4m 47s
win+VS build	-1s
win+Meson build	4m 30s
documentation	7m 8s
osx-gcc (macos-14)	6h 0m 16s
osx-meson (macos-14)	54m 46s
static-analysis	6m 6s
osx-reftable (macos-14)	35m 51s
osx-clang (macos-14)	6h 0m 16s
sparse	3m 55s
rust-analysis	1m 31s
debian-11 (debian:11)	21m 54s
almalinux-8 (almalinux:8)	19m 22s
linux-sha256 (ubuntu:rolling)	18m 48s
fedora-breaking-changes-meson (fedora:latest)	18m 3s
linux-leaks (ubuntu:rolling)	49m 4s
linux-reftable (ubuntu:rolling)	28m 7s
linux-musl-meson (alpine:latest)	23m 27s
linux-TEST-vars (ubuntu:20.04)	23m 43s
linux-asan-ubsan (ubuntu:rolling)	1h 8m 16s
linux-meson (ubuntu:rolling)	26m 13s
linux-breaking-changes (ubuntu:rolling)	18m 37s
linux-reftable-leaks (ubuntu:rolling)	47m 6s
linux32 (i386/ubuntu:focal)	6h 0m 4s
win+VS test	0s
win+Meson test (0)	6m 54s
win+Meson test (7)	7m 23s
win+Meson test (4)	6m 11s
win+Meson test (1)	10m 35s
win+Meson test (3)	10m 32s
win+Meson test (8)	8m 45s
win+Meson test (9)	6m 34s
win+Meson test (2)	58m 58s
win+Meson test (6)	12m 4s
win+Meson test (5)	8m 32s
win test (1)	6m 40s
win test (4)	13m 27s
win test (2)	9m 35s
win test (7)	6m 40s
win test (3)	56m 59s
win test (5)	11m 20s
win test (6)	7m 29s
win test (0)	11m 39s
win test (9)	5m 6s
win test (8)	7m 14s
	1d 6h 35m 43s

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