Further updates to v14 upgrade doc

[rmccue]

@mikelittle does this also need backporting to master?

[hm-backport[bot]]

The backport to master failed:

Commits ["5cf79ec8c40697bcfe4307eef0e02def41738bc2","c3e9261b0aa49b46ef810a72265123661a951d55","8f45109f75bc768890c3d0f232330705704b309f","3cbd06e9861c065e897d22d7006494cb225c93a2","3fb66247e060fdc7e405c8a7b7c54decea083857","841b0b4dc94eefc329ce643df59c0d429b2ef545","1bace4ddbfe8629adff84211e4cfbaa453ae2753","0e622474e5b184e10a8d5fc1c5e06173d670a00e"] could not be cherry-picked on top of master

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub.
git fetch
# Create new working tree.
git worktree add .worktrees/backport master
# Navigate to the new directory.
cd .worktrees/backport
# Cherry-pick all the commits of this pull request and resolve the likely conflicts.
git cherry-pick 5cf79ec8c40697bcfe4307eef0e02def41738bc2 c3e9261b0aa49b46ef810a72265123661a951d55 8f45109f75bc768890c3d0f232330705704b309f 3cbd06e9861c065e897d22d7006494cb225c93a2 3fb66247e060fdc7e405c8a7b7c54decea083857 841b0b4dc94eefc329ce643df59c0d429b2ef545 1bace4ddbfe8629adff84211e4cfbaa453ae2753 0e622474e5b184e10a8d5fc1c5e06173d670a00e
# Create a new branch with these backported commits.
git checkout -b backport-462-to-master
# Push it to GitHub.
git push --set-upstream origin backport-462-to-master
# Go back to the original working tree.
cd ../..
# Delete the working tree.
git worktree remove .worktrees/backport

Then, create a pull request where the base branch is master and the compare/head branch is backport-462-to-master.

[kovshenin]

I think these changes were done on master in other commits and PRs. The only difference I see now between v14-branch and master is in other-docs/guides/updating-php/README.md, will resolve that in a separate PR.