The Manifest.toml file is committed to the repo to allow replicating the exact branches.
pkg> instantiate
pkg> update
$ cd to/this/apps/directory
$ julia --project
julia> using Genie
julia> Genie.go()
Alternatively you can run $ ./bin/repl
or $ ./bin/server
for your OS to start the repl with the app loaded -- or respectively the server.