foreman: allow using substitutes by default

foreman/start-hydra.sh

@@ -8,5 +8,11 @@ createdb -h $(pwd)/.hydra-data/postgres -p 64444 hydra
 hydra-init
 hydra-create-user alice --password foobar --role admin
 
-touch .hydra-data/hydra.conf
+if [ ! -f ./.hydra-data/hydra.conf ]; then
+    echo "Creating a default hydra.conf"
+    cat << EOF > .hydra-data/hydra.conf
+# test-time instances likely don't want to bootstrap nixpkgs from scratch
+use-substitutes = true
+EOF
+fi
 HYDRA_CONFIG=$(pwd)/.hydra-data/hydra.conf exec hydra-dev-server --port 63333