make use of DNS throughout the documentation

[rade]

ATM the weaveDNS documentation is completely separate from the main documentation, with just the odd reference to it from the latter. This was desirable when weaveDNS was new and experimental, but now it actually hinders adoption.

The weave 1.0 walkthrough in #242 presents a much more integrated view of weaveDNS, and hence can serve as guidance for this issue, though we won't be able to go quite as far until a few more features have landed.

[rade]

What is happening with this?

[rade]

I've just noticed that our main docs page does not mention WeaveDNS at all!

[errordeveloper]

@rade I believe this should still be open, as you said.

[rade]

Where we want to get to here is that pretty much all our examples in the docs use names instead of IP addresses for addressing containers.

Ideally we want to tackle this after #383, #749, #750, #762, #763.

It is also related to #869.

We will still want to keep a dedicated piece of weaveDNS documentation, to cover all the various exotic uses, troubleshooting, etc.