git: openjdk/jdk: 8312882: Update the CONTRIBUTING.md with pointers to lifecycle of a PR

[Jesper Wilhelmsson]

Changeset: 42758cb8
Author:    Jesse Glick <jglick at cloudbees.com>
Committer: Jesper Wilhelmsson <jwilhelm at openjdk.org>
Date:      2023-08-10 22:26:32 +0000
URL:       https://git.openjdk.org/jdk/commit/42758cb889a5cf1d7f4c4b468a383b218baa1b27

8312882: Update the CONTRIBUTING.md with pointers to lifecycle of a PR

Reviewed-by: erikj, jwilhelm

! CONTRIBUTING.md
! doc/building.html
! doc/building.md