swap 12 and 13

part13/README.md

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+Part 13
+=======
+
+## Installation
+
+```bash
+elm package install
+```
+
+(Answer `y` at the prompt. In rare cases a known issue can cause the download
+to fail; in that case, just run `elm package install` again.)
+
+## Building
+
+```bash
+elm live Main.elm --open -- --output=elm.js
+```
+
+## Compiling CSS
+
+```bash
+elm css Stylesheets.elm
+```