[Feature Request] Make mergerfs.balance be aware of hard links

[xsm1997]

I use hard links frequently. So, it will be awesome for mergerfs.balance to ignore files with multiple links (e.g., hard links), because moving those files to another partition will leads to duplicate space occupy. You can get this property in stat command or function.

You can detect all instances of those files, and move all of them to another partition, of course. But if it is too complicated, you can simply ignore those files.

[erikhubers]

I just fell into this trap and now duplicated a lot of files. Can we at least put a warning in the documentation so morons like me don't make the mistake of using this tool when also using hardlinks extensively