I second the motion for ADRs (resources below). A side-benefit is that they use Markdown: plain and simple. Try to use Markdown (or similar) as much as possible. Once you are used to it, it is hard to go back to the insane formatting friction in a word processor.

[1] - http://thinkrelevance.com/blog/2011/11/15/documenting-archit... [2] - https://www.youtube.com/watch?v=LMBqGPLvonU