add eval example

packages/eval/README.md

@@ -9,6 +9,33 @@ It allows creating strudel patterns from input code that is optimized for minima
 npm i @strudel.cycles/eval --save
 ```
 
+## Example
+
+```js
+import { evaluate, extend } from '@strudel.cycles/eval';
+import * as strudel from '@strudel.cycles/core';
+
+extend(strudel); // add strudel to eval scope
+
+async function run(code) {
+  const { pattern } = await evaluate(code);
+  const events = pattern.firstCycle();
+  console.log(events.map((e) => e.show()).join('\n'));
+}
+
+run('sequence([a3, [b3, c4]])');
+```
+
+yields:
+
+```js
+(0/1 -> 1/2, 0/1 -> 1/2, a3)
+(1/2 -> 3/4, 1/2 -> 3/4, b3)
+(3/4 -> 1/1, 3/4 -> 1/1, c4)
+```
+
+[play with @strudel.cycles/eval on codesandbox](https://codesandbox.io/s/strudel-eval-example-ndz1d8?file=/src/index.js)
+
 ## Dev Notes
 
 shift-traverser is currently monkey patched because its package.json uses estraverse@^4.2.0,