Re-introduce demo docs (#1981)

Document the included samples in the docs again so there's some continuity from v1 docs, while making it clear they're not best practice examples but instead illustrate solutions to various use-cases.

docs/source/building-a-cordapp-index.rst

@@ -11,3 +11,4 @@ CorDapps
    corda-api
    flow-cookbook
    cheat-sheet
+   building-a-cordapp-samples

docs/source/building-a-cordapp-samples.rst

@@ -0,0 +1,21 @@
+CorDapp samples
+===============
+
+There are two distinct sets of samples provided with Corda, one introducing new developers to how to write CorDapps, and
+more complex worked examples of how solutions to a number of common designs could be implemented in a CorDapp.
+The former can be found on `the Corda website <https://www.corda.net/samples/>`_. In particular, new developers
+should start with the :doc:`example CorDapp <tutorial-cordapp>`.
+
+The advanced samples are contained within the `samples/` folder of the Corda repository. The most generally useful of
+these samples are:
+
+1. The `trader-demo`, which shows a delivery-vs-payment atomic swap of commercial paper for cash
+2. The `attachment-demo`, which demonstrates uploading attachments to nodes
+3. The `bank-of-corda-demo`, which shows a node acting as an issuer of assets (the Bank of Corda) while remote client
+   applications request issuance of some cash on behalf of a node called Big Corporation
+
+Documentation on running the samples can be found inside the sample directories themselves, in the `README.md` file.
+
+.. note:: If you would like to see flow activity on the nodes type in the node terminal ``flow watch``.
+
+Please report any bugs with the samples on `GitHub <https://github.com/corda/corda/issues>`_.

docs/source/quickstart-index.rst

@@ -7,4 +7,5 @@ Quickstart
    getting-set-up
    tutorial-cordapp
    Sample CorDapps <https://www.corda.net/samples/>
+   building-against-master
    CLI-vs-IDE