Well a search here in the forum throws up quite some entries
https://discourse.osmc.tv/search?q=NFS%20server
And based on this post it is as easy as sudo apt-get install nfs-kernel-server
Currently NFS Server is not in the App Store and you would need to configure it manually for your shares.
To be honest if you are not that experienced with installing NFS Servers under Debian you might want to stick to the Samba Server in the App Store.