[Doc] Update documentation for no-transitive-change (#96453)
(Some backgrounds, not required to read:
https://discourse.llvm.org/t/rfc-c-20-modules-introduce-thin-bmi-and-decls-hash/74755)
This is the document part for the no-transitive-change
(https://github.com/llvm/llvm-project/pull/86912,
https://github.com/llvm/llvm-project/pull/92083,
https://github.com/llvm/llvm-project/pull/92085,
https://github.com/llvm/llvm-project/pull/92511) to provide the ability
for build system to skip some unnecessary recompilations.
See the patch for examples.