Update HDF5 build documentation to preserve useful information associated with Autotools

Some information useful for both Autotools and CMake may be removed along with Autotools in #5358. See the review comments in the PR. It may need minor revision for CMake only.

- bin/release line ~312 comments - retain modified check for running in top-level directory?
- release_docs/RELEASE_PROCESS needs another review to remove any obsolete entries for autotools only, and to
revise for CMake any that were written for Autotools but are still needed with CMake.
- README.md line ~20 - useful information deleted that should be kept, but needs revision for CMake only