Backport upgrade guide improvements

[mikelittle]

Back ports the missing updates to the v16 upgrade guide.

[hm-backport[bot]]

The backport to master failed:

Commits ["fbacf9f5ab0d075064ab11705f3a4d6e584b09ad"] 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 fbacf9f5ab0d075064ab11705f3a4d6e584b09ad
# Create a new branch with these backported commits.
git checkout -b backport-532-to-master
# Push it to GitHub.
git push --set-upstream origin backport-532-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-532-to-master.