[Doc] Update documentation for no-transitive-change

[ChuanqiXu9]

(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.

CC: @mathstuf @boris-kolpackov