Global Fallback Justfile
A global fallback justfile may be set with --global-fallback-justfile <PATH>,
or by setting the JUST_GLOBAL_FALLBACK_JUSTFILE environment variable.
If no justfile is found, or if the search for a fallback does not succeed, the
global fallback justfile is used instead. The working directory is set to the
root of the current project, as determined by the presence of a directory like
.git, or the invocation directory if no such directory is found. The global
fallback justfile may itself use set fallback.
The global fallback justfile is ignored when --justfile, --global-justfile,
or --working-directory is passed.