Update upgrade-from-v0.6.2-to-v0.7.0.md
Update upgrade-from-v0.6.2-to-v0.7.0.md

Add recreate storage class step

Signed-off-by: Sheng Yang <147fd7034704a96aa91f641610a6d7a9748e39bc@rancher.com>
rancher/longhorn