Fix warning of implicit declaration of function 'strcasestr'

According to manpage of strcasestr [1], the macro function needs to be added.

[1] https://linux.die.net/man/3/strcasestr

Signed-off-by: SZ Lin (林上智) <szlin@debian.org>

It seems the behaviour of the default opener (xdg-open) varies across platforms
and environments. Details are documented in the issue. To prevent an empty file
from being accidentally opened leading to unexpected behaviour, we are adding a
guard with the message that the empty file should be opened using edit or open
option.

Update README.md -Milis

Milis Linux support

Milis Linux support

Fix a broken link

Document how to install fish quitcd function

It was not clear that the name of the file should match
the name of the function.