added ASGI docs

Author: dantownsend

docs/src/index.rst

@@ -13,6 +13,7 @@ Welcome to Piccolo's documentation!
    piccolo/engines/index
    piccolo/migrations/index
    piccolo/authentication/index
+   piccolo/asgi/index
    piccolo/features/index
    piccolo/playground/index
    piccolo/ecosystem/index

docs/src/piccolo/asgi/index.rst

@@ -0,0 +1,28 @@
+.. _ASGI:
+
+####
+ASGI
+####
+
+Using Piccolo standalone is fine if you want to build a data science script,
+but often you'll want to build a web application around it.
+
+`ASGI <https://asgi.readthedocs.io/en/latest/>`_  is a standardised way for
+async Python libraries to interoperate. It's the equivalent of WSGI in the
+synchronous world.
+
+By using the ``piccolo asgi new`` command, Piccolo will scaffold an ASGI web
+app for you, which includes everything you need to get started.
+
+Currently, `Starlette <https://www.starlette.io/>`_  is used as the routing framework, and is a great choice.
+
+Other great ASGI routing frameworks exist, and may be supported in the future
+(`Quart <https://pgjones.gitlab.io/quart/>`_ ,
+`FastAPI <https://fastapi.tiangolo.com/>`_ ,
+`Sanic <https://sanic.readthedocs.io/en/latest/>`_ ,
+`Django <https://www.djangoproject.com/>`_  etc).
+
+`Hypercorn <https://pgjones.gitlab.io/hypercorn/>`_ and
+`Uvicorn <https://www.uvicorn.org/>`_  are available as ASGI servers.
+`Daphne <https://github.com/django/daphne>`_ can't be used programatically so
+was omitted at this time.