introduce users how to use flox to self-update flox

[robinbrantley]

There are different ideas on how to get the word out but I will limit this issue to these 3:

1. put it in floxdocs (more than just the command - expand upon it with additional explanation/wording based on the notes below)
2. write up a small blog on it
3. announce in discourse (Robin can assist / do that once either 1 or 2 are completed)

Grabbing the info from slack chat on Wed 7 June:

• And while we're on the subject I realize this should feature prominently in our docs. We should invite our users to add eval "$(flox activate -e flox/default)" to their appropriate "dotfile" to stay up-to-date with our production releases, or add eval "$(flox activate -e flox/prerelease)" to make use of "bleeding edge" versions hot off the press.

• Note that this is different to updating the installed version of flox, you are using flox to update flox in a flox environment. ie, when you flox activate -e flox/default your installed flox remains the same (as in when you install flox via apt, rpm ... ) but you are updating the flox package in your flox env, just like you would any other package in your env.

• We can think of the "system flox" as bootstrapping the one that users [optionally] activate and run from the flox/{default,prerelease} environments. It's not dissimilar to "system python" that comes with your RHEL distribution and is used for system initfiles, etc. as opposed to the "local" python maintained in /opt or /usr/local or wherever. Nobody uses the "system python" for production use, but they all expect it to be there as a backstop and available for use when booting a machine; our "system flox" will be the same.

• The bottom line:

  • people will want to update their "system flox" by way of the usual apt, dnf, yum, etc. methods, and notably this is what upgrades the version of the running nix-daemon
  • people can get access to a self-updating, fresher version of flox by using the flox-maintained flox/{default,prerelease} environments in the meantime

Also note that some shells apparently hang on the above command so you may need to instead add eval "$( flox activate -e flox/prerelease; )"; to your dot file (I think this is true for .zsh?)