move implemented design for 1.18

Signed-off-by: Lyndon-Li <lyonghui@vmware.com>

changelogs/CHANGELOG-1.18.md

@@ -16,7 +16,7 @@ https://velero.io/docs/v1.18/upgrade-to-1.18/
 #### Concurrent backup
 In v1.18, Velero is capable to process multiple backups concurrently. This is a significant usability improvement, especially for multiple tenants or multiple users case, backups submitted from different users could run their backups simultaneously without interfering with each other.  
 
-Check design https://github.com/vmware-tanzu/velero/blob/main/design/concurrent-backup-processing.md for more details.
+Check design https://github.com/vmware-tanzu/velero/blob/main/design/Implemented/concurrent-backup-processing.md for more details.
 
 #### Cache volume for data movers
 In v1.18, Velero allows users to configure cache volumes for data mover pods during restore for CSI snapshot data movement and fs-backup. This brings below benefits:
@@ -24,7 +24,7 @@ In v1.18, Velero allows users to configure cache volumes for data mover pods dur
 - Solve the problem that multiple data mover pods fail to run concurrently in one node when the node's ephemeral disk is limited
 - Working together with backup repository's cache limit configuration, cache volume with appropriate size helps to improve the restore throughput
 
-Check design https://github.com/vmware-tanzu/velero/blob/main/design/backup-repo-cache-volume.md for more details.
+Check design https://github.com/vmware-tanzu/velero/blob/main/design/Implemented/backup-repo-cache-volume.md for more details.
 
 #### Incremental size for data movers
 In v1.18, Velero allows users to observe the incremental size of data movers backups for CSI snapshot data movement and fs-backup, so that users could visually see the data reduction due to incremental backup.