Dub documentation with an initial ddoc file

[Conor O'Brien via Digitalmars-d-learn]

I've been trying to figure out how to generate documentation for 
my project using dub. I have found this link[1] which told me how 
I could use dub to generate docs:

     dub build --build=docs <project-name>

However, I wish to have a set of macros that are present on every 
documentation file, that would define how the resultant HTML 
document is rendered. I tried:

     dub build --build=docs <project-name> html.ddoc

But I got the following error:

     Expected one or zero arguments.
     Run "dub build -h" for more information about the "build" 
command.

How might I include `html.ddoc` with every file that has 
documentation?

[1]: 
https://stackoverflow.com/questions/29762668/using-dub-to-build-documentation