doc: PG 16 relnotes, initial markup

Bruce Momjian <bruce@momjian.us>

Commit: 6b86a3e0b421a0e0c9cfa02ddc0525e431379ee4
Author: Bruce Momjian <bruce@momjian.us>
Date: 2023-08-16T18:34:49Z
Releases: 16.0
doc:  PG 16 relnotes, initial markup

Still need to add links to doc sections.

Backpatch-through: 16 only

Files

PathChange+/−
doc/src/sgml/release-16.sgml modified +273 −274

Documentation touched