If you've mounted your share to /media/nfsshare1
on your host OS and you can write to it from within Linux, you should just be able to bind mount /media/nfsshare1
to a directory within your container in the same way you do a non-NFS local path - under the Volumes tab in Advanced container settings when creating a container, or in your stack yaml. As far as Docker will be concerned, it is a local path - since the mounting is done at the OS level through fstab, Docker has no idea what it actually is underneath.
If on the other hand you want to create a NFS volume in Portainer, you wouldn't do the mounting via fstab and instead do it all in the Create volume page (or in your stack yaml).