generate a mips squashfs with some s6-rc services

haven't even tried booting it but I don't expect it to work. Needs

- s6-linux-init or some other pid 1 program
- a kernel

tools/builder.sh

@@ -0,0 +1,16 @@
+source $stdenv/setup
+mkdir -p $out/${name}
+echo $type > $out/${name}/type
+mkdir -p $out/${name}/dependencies.d
+echo $buildInputs > $out/buildInputs
+test -n "$dependencies" && for d in "$dependencies"; do
+    touch $out/${name}/dependencies.d/$d
+done
+test -n "$contents" && for d in "$contents"; do
+    mkdir -p $out/${name}/contents.d
+    touch $out/${name}/contents.d/$d
+done
+test -n "$run" && (echo "$run" > $out/${name}/run)
+test -n "$up" && (echo "$up" > $out/${name}/up)
+test -n "$down" && (echo "$down" > $out/${name}/down)
+(echo  $out/${name} && cd $out/${name} && find . -ls)