First be sure that the NFS service is running on the Synology
Either use an existing shared folder or create a new one for the NFS data:
(I am marking the “Hide this shared folder in “My Network Places” to not show it to other users)
I will make admin able to connect through CIFS for easy recovery-jobs
Open the NFS Privileges dialog – Create
Type in your ESXi/ESX host ip(NFS kernel ip) and make it read/write
Now setup on the Synology Diskstation is done – continue on to the ESXi host through the vSphere Client(or vCenter):
Under the tab Configuration, select Storage and press Add Storage…
Select Network File System –>
Server is the ip or dns-name of the Synology, Folder is the path to the NFS-folder which will be /volume1/”folder name” here /volume1/NFS and click Next, verify and click Finish 
Now there is an NFS datastore available for the ESXi host