armadaproject.io: Make it possible to develop via a fork

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In my recent work on armadaproject.io, I discovered that some of the HTML files contain direct URLs to assets needed. In order to develop this in a github pages fork, we need to be able to adjust those URLs to contain prefixes.

e.g.:
https://jayofdoom.github.io/assets/img/brand/armada-under-shadow.svg 404s, because it did not add in the /armada needed (whereas https://jayofdoom.github.io/armada/assets/img/brand/armada-under-shadow.svg works).

Determine how to do this, and document a development process that involves github in the readme.txt for future developers. There are already limited instructions there pointing out this limitation.

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