docs: add v0.40 rewrite plan #269

Job	Run time
release	12s
build (windows-latest, x86_64-pc-windows-msvc)	11m 12s
build (ubuntu-24.04, x86_64-unknown-linux-gnu)	5m 26s
build (macos-latest, aarch64-apple-darwin)	10m 52s
build (macos-latest, x86_64-apple-darwin)	4m 48s
	32m 30s

Provide feedback