Proposal: Adding README to explain examples

[GSORF]

This is a README which shows an overview of (and explains) the available examples.

It is currently Work in Progress, so please give me some time to write up a few instructions for starters. Here is a little TODO list I am trying to complete before asking for approval:

• Prepare general structure of README (Hardware setup, Tutorial content by listing individual example scripts)
• Add link to Cannot connect to roscore from android phone #39
• Add link to Error while registering publisher /rosout: Connection refused #46
• Add illustration for hardware setup (Smartphone + Flutter, Router, Laptop + ROS - each annotated with IP Address and ROS Master / Hostname / IP)
• Rename example scripts using scheme 01_XYZ.dart to 08_XYZ.dart in order to ensure structure with some tutorial progression for starters.
• Add Links to the example scripts
• Explain all example scripts
• Find out how to generate "Image" message (and other custom messages) - does a ready-to-use flutter package exist for the 'package:sensor_msgs/msgs.dart' on pub.dev? Maybe kindly ask @TimWhiting if there is some way without custom compilation using a dedicated ROS installation (i.e. we want some easy solution for beginners without the need to install ROS on a linux system)

[TimWhiting]

Thanks! 🎉