Improve quickstart for Programming the Cloud

[lindydonna]

• Add back serverless example
• Change current Programming the Cloud tutorial to Programming containers
• Address Luke's high-level feedback below

1. The Programming the Cloud section no longer really feels like programming the cloud - there are no high level managed services being programmed here (like Table or HttpEndpoint or Topic or even Function). I suggest we'll want to have three top level sections: (1) Programming AWS (2) Programming containers (3) Programming the Cloud.
2. The container example is nice and relatable - but perhaps too relatable again in a different direction it's not clear why this is any better than a similar docker-compose example. In fact, as written, I'd say it's tenuous that it actually is better. There's a subtle (but important) point that it is better because of the build support even when targeting a production environment - I think we will need to explain the core to what's different here - and why that difference is central to what makes Pulumi unique (not just another one off thing we did "differently") - which I believe is true - the core model that cloud applications are made up of both application and infrastructure code which can and should in many cases version together - the same thing that motivates lambdas as lambdas and our overall @pulumi/cloud model. There's also the claimed benefit that we allocate the ECS cluster for you - but that's really an antipattern - you shouldn't be deploying a whole cluster just to host a single app! The real "magic" of the container support is that it can be combined with the rest of our offerings, in both direction - fixed AWS infrastructue as well as high level functions, APIs, tables etc.
3. Related to these points - this makes me even more eager to get to the one example which really highlights Pulumi all up at once - something that feels more like what we've used for LM or for our PPC or even in the containers unit test. Something that is really more fundamentally uniquely "Pulumi".

[lindydonna]

Bringing back serverless example is tracked by #117. The rest will be covered by planned quickstart work.