FSLeyes plugin installation will break with non-bash SHELL

[jcohenadad]

Currently, installation says:

This will not work with ppl having non-bash shell (eg zsh, which is now default on macOs). And some of our users won't understand why it will fail.

Solutions:

1. We explain different scenario depending on the shell (zsh, bash, etc.)
2. We simply ask to reopen a new Terminal.

I prefer option 2.

[gaspardcereza]

I also prefer option 2. And people with good bash/zsh knowledge will probably guess that they can get the same result by typing source ~/.bashrc or whatever it is on zsh