update changelog for v0.8.0 (#3382)
update changelog for v0.8.0 (#3382)

* update changelog for v0.8.0

Signed-off-by: Wenqi Li <8ba7dfe933ef10910139377fbe2efeb7f8f88b49@nvidia.com>

* update based on comments

Signed-off-by: Wenqi Li <8ba7dfe933ef10910139377fbe2efeb7f8f88b49@nvidia.com>

Co-authored-by: Nic Ma <b0dc69321d91891b55520ef34f868910ffd06e02@nvidia.com>
Project-MONAI/MONAI,Project-MONAI/MONAI,Project-MONAI/MONAI,Project-MONAI/MONAI