Write the readme

[fer-rum]

A "Readme" file is the essence of a project - most often its first interface to the outside world.
Therefore such a file should contain at least an overview over

• what the project does
• who develops it
• where to find additional information

Links are also nice.

[HirokiKibori]

A style-guide and architecture-policies are also important for contributions. (A fourth section.)