Rename more stuff

intro/part9/README.md

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+# Part 9
+
+To build everything, `cd` into the `part9/` directory and run:
+
+```shell
+elm-live src/Main.elm --output=../server/public/elm.js --dir=../server/public --pushstate
+```
+
+Then open [http://localhost:3000](http://localhost:3000) in your browser.
+
+## Exercise
+
+Open `src/Ports.elm` in your editor and resolve the TODOs there.
+