Extend adduser question to include explanation on how to separate the groups to join the new user

[bcr]

Summary

During the non-root user setup (adduser.sh), people are often confused what the separator is when they are asked which groups to join the new user into. For example, wheel and operator. Users often assume that it is separated by a comma (and maybe even a space after it), but the script will check for that and refuse such entries.

Help the users by mentioning that the groups need to be space separated in the question itself. That way, it does not take up extra space and avoids confusion about what the separator is.

Test Plan

1. Apply patch
2. Run adduser.sh
3. Check the question about "inviting the new user into other groups"
4. Comment or approve

[bcr]

The whitespace change after the fi was unintentional, but while I was there, I fixed it, too.

[jrm]