Add comment about backing up in 0.8 upgrade guide
Add comment about backing up in 0.8 upgrade guide

Signed-off-by: JoshVanL <525f14a1257c4e494fcfb5b458ace90de1e9c01d@gmail.com>

cert-manager/cert-manager,jetstack/cert-manager,jetstack-experimental/cert-manager,jetstack/cert-manager,cert-manager/cert-manager,jetstack/cert-manager,jetstack-experimental/cert-manager,jetstack-experimental/cert-manager,cert-manager/cert-manager