Could use a page describing upgrade instructions

From an IRC conversation, @jperkin outlined it as:

"we set varbase to /var so the only thing you usually need to back up is any configs you've modified under /opt/local/etc

so save those out, wipe out /opt/local (and /var/db/pkgin for good measure), unpack new bootstrap, pkgin , restore /opt/local/etc/foo.conf and off you go

config files are normally handled by the original going into share/examples and then copied into etc, so it's not too difficult to script up a diff to show you what you

copies are only done if there is no existing conf, so an alternative is to simply restore the configs before pkgin and then they won't get overwritten

but then you need to handle applications which change config format etc"

Use the quoted IRC upgrade procedure as the source material for a new documentation page. Cover backing up modified files under /opt/local/etc, removing the old installation, unpacking the new bootstrap, reinstalling packages with pkgin, and restoring configuration; done means the upgrade steps are clearly documented.