Docs: Added a command for magic support when using fish

[0123takaokeita]

I found that some commands failed when I executed them as described in the readme.

I found out that the writing style is different for fish.

I ran into this because I was using fish, but how about adding this for others?

fail

success

[mxcl]

With v1 we need shellcode for fish (fresh). We also typically recommend eval "$(tea foo)" now which is POSIX portable.