Add favicon and logo documentation

[Zaijo]

Add documentation for #135

[Zaijo]

@jp7677 can you please correct the documentation so it documents real steps?

[Zaijo]

It's ready from my side. Working for me as documented.

[jp7677]

Thanks a lot for taking the initiative. Would you mind expanding the documentation to include all the branding properties? I think it is also a good idea to start with an introduction and a table showing the separate properties and its meanings.

[Zaijo]

I'm not aware of any other options. Do you have some link with details? On the other hand, this is quite the maximum I'm able to offer these days.

[jp7677]

The other two options are the primary and secondary colors, next to the properties that Structurizr itself offers for the C4-Plantuml exporter.
See https://github.com/avisi-cloud/structurizr-site-generatr/blob/main/docs/example/workspace.dsl#L159 and https://github.com/structurizr/export/tree/main/src/main/java/com/structurizr/export/plantuml#c4plantumlexporter

[Zaijo]

Sorry, no more time on my side.

[jp7677]

Superseded by #206