split static structure (scripts) from modifiable/updatable user data (stones)

[dalehenrich]

@DamienCassou is working on building a Nix package for GsDevKit_home as a prerequisite to working on Issue #22.

The model for GsDevKit_home that @DamienCassou is using is based on having the static structure (primarily scripts) installed in a readonly component while the modifiable data (stones, pharo images, git repos, etc.) would be installed in a user's directory structure ...

I agree that this is a good structure to use.

The plan is to create a sysAdmin branch with the static structure and a user branch with the modifiable data .... over time, the _home project will migrate toward using this model by default ...