fix up makefile, include install target

Makefile

@@ -1,3 +1,12 @@
+result:
+	nix-build -A build
+
+install: result
+	nix-env -i "$$(readlink result)"
+
+clean:
+	rm result
+
 serve:
 	nix-shell -A serve
 
@@ -6,6 +15,3 @@ update:
 
 lock:
 	nix-shell -p bundler -p bundix --run 'bundler lock; bundler package --no-install --path vendor; bundix; rm -rf .bundle vendor'
-
-build:
-	nix-build -A build

build.sh

@@ -1,5 +1,6 @@
 source $stdenv/setup
 set -e
 
-mkdir -p "$out"
-$jekyll_env/bin/jekyll build -s "$src" -d "$out"
+d="$out/var/www/blog.mediocregopher.com"
+mkdir -p "$d"
+$jekyll_env/bin/jekyll build -s "$src" -d "$d"