Add instructions for usage with /etc/fstab

[daniel-santos]

So this was a bit of a pain and I figured I should pass on what I've learned. I am now able to have whatever desktop environment do mount & umount from the gui tool after adding this to fstab:

jmtpfs          /media/g2       fuse            rw,users,noauto         0 0

The very important part is users and not user. Otherwise, as non-root, I can mount /media/g2 and I can fusermount -u /media/g2, but I cannot umount /media/g2, which is what the desktop gui seems to like to do.

This information would probably be helpful for README.md