Add documentation for templating in docker container

[amir-zeldes]

Using docker's -v option allows injection of static directory structures from outside the container, we should:

1. Document how this works
2. Maybe provide a simple templating example showing how to set a project name and a basic color scheme (e.g. a Bootstrap theme?)

[lgessler]

Maybe it'd be better for us to scrub GitDox of SCRIPTORIUM-specific theming and provide a sensible default theme so our users wouldn't have to repeat that work? I couldn't see that taking more than 5 hours.

[amir-zeldes]

Semi-done in 6b37921, maybe we should still remove the GU logo