Update PROFILE_FILE for system when running as root

[freef4ll]

Running a global system install like:

sudo SWIFTLY_HOME_DIR=/usr/local/share SWIFTLY_BIN_DIR=/usr/local/bin ./swiftly-install.sh  --disable-confirmation

Will result the profile being added for the root user, but can include this globally for all users by creating a file in /etc/profile.d

[patrickfreed]

The root user may still want to install packages just for themselves, so I don't know if we want to gate this behavior on that. However, I think it does make sense to have a configuration option to allow for system-wide installs. Does that sound good to you?

[freef4ll]

Yep, configuration option is good!