Add a README about using the examples

Author: evancz

examples/README.md

@@ -0,0 +1,20 @@
+# Run the Examples
+
+To try these examples out locally, you can run the following terminal commands:
+
+```bash
+git clone https://github.com/elm/parser.git
+cd parser/examples
+elm reactor
+```
+
+After that, go to [`http://localhost:8000`](http://localhost:8000) and click on
+the example you want to see.
+
+
+## Exercises
+
+- Have a user input feed into the `Math` parser. Show people the results live.
+- Expand the `Math` parser to cover `-` and `/` as well.
+- Handle more escape characters in `DoubleQuotedString`. Maybe hexidecimal
+escapes like `\x41` and `\x0A` that are possible in JavaScript.