Add network upgrade notes for CNI

[computator]

This addresses containers/podman#17048

[rhatdan]

LGTM @TomSweeneyRedHat PTAL

[lsm5]

@computator LGTM, but before we merge, could you please add your signoff on the commit ?

[TomSweeneyRedHat]

LGTM, once signed (git commit --amend -s, git fetch --all, git rebase upstream/main, git push ....)

[computator]

Updated!