Fix erroneous references, remove whitespace, remove references to so-far unimplemented links.
Merge remote-tracking branch 'refs/remotes/origin/master' into introduction-fixes-436
Address review comments: flocker-node removed, formatting, explanation of handed off.
Address review comment: Refer to nodes, not machines.
Address review comment: NAT is not exciting.
Merge pull request #443 from ClusterHQ/introduction-fixes-436

Introduction improvements.

Fixes #436.