Add part4

advanced/part4/README.md

@@ -0,0 +1,13 @@
+# Part 4
+
+To build everything, `cd` into this `part4/` directory and run:
+
+```shell
+elm make src/Main.elm --output=../server/public/elm.js
+```
+
+Then open [http://localhost:3000](http://localhost:3000) in your browser.
+
+## Exercise
+
+Open `src/Article/Feed.elm` in your editor and resolve the TODO there.