build

docs: improve md format for `jj fix` #13644

Job	Run time
Build jj-lib without Git support	45s
build (ubuntu-latest)	4m 34s
build (macos-13)	5m 29s
cargo-deny (advisories)	25s
build (macos-14)	5m 28s
cargo-deny (bans licenses sources)	27s
build (windows-latest)	9m 35s
build (ubuntu-latest, --all-features)	5m 38s
Check protos	25s
Check that MkDocs can build the docs	27s
Check that MkDocs can build the docs with Poetry 1.8	20s
Clippy check	2m 33s
Check formatting	15s
	36m 21s

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