The opening brace '{' can't begin a line. This was causing the script to fail.
You don't need '/' inside of scripts, you can have them if you like, but they are not needed.
Corrected script.
on ^*:JOIN:#mychannel:{
var %person = $read(people.ini)
if ($readn == 0) {
notice $nick Good day!
write people.ini $nick
}
}