add async info

notes.md

@@ -17,3 +17,40 @@
   * async
   * better exception handling
   * randomise output filename
+
+### Async bits
+
+in `__main__`:
+
+```python
+loop = asyncio.get_event_loop()
+try:
+    loop.run_until_complete(main())
+finally:
+    loop.close()
+```
+
+  * initialises loop and runs it to completion
+  * needs to handle errors (try/except/finally)
+
+```python
+async def run(args=None):
+    tasks = []
+
+    for url in pool:
+        tasks.append(url)
+    # for i in range(10):
+        # tasks.append(asyncio.ensure_future(myCoroutine(i)))
+
+    # gather completed tasks
+    await asyncio.gather(*tasks)
+```
+
+Getting the contents of the page needs to be async too
+
+```python
+async def get_source():
+    blah
+    blah
+    await urlopen(url)
+```