gitian: update descriptors to use a sane uniform output
release: update docs to reflect new layout

- Split linux32/linux64 releases
- Split win32/win64 zips
- Post-processing should no longer be required. The deterministic outputs are
  ready for consumption.
Merge pull request #5371

dfef929 release: update docs to reflect new layout (Cory Fields)
52bb7a7 gitian: update descriptors to use a sane uniform output (Cory Fields)