Add extra examples

[bartbutenaers]

Add hello world example (see here) to the readme page. And a a list of extra readme pages, which contain more advanced examples.

[bartbutenaers]

@cymplecy,

I have added a couple of example flows as json files in a new "examples" folder in this repository:

This way the examples become available via the Node-RED flow editor "Import" menu:

If you have any other flows available, you can add them both on the wiki and as json files.
It seems that most of our wiki pages have no json definitions of the flows being created...
I have only added a json flow definition to the Hello World wiki page.