install CHANGELOG.md

MSP-11103

CHANGELOG.md template for categories of changes.
install UPGRADING.md

MSP-11103

Just a stub for adding Deprecation and Incompatible Changes upgrade
information later.
Add CHANGELOG.md updating to RELEASING.md

MSP-11103

Explain categories in CHANGELOG.md and how to update the CHANGELOG.md,
then use the CHANGELOG.md for Next Release to inform how to update
`VERSION`.
Add prepping CHANGELOG.md for next release to RELEASING.md

MSP-11103