Add Maintenance Documentation

Hi there! I have worked on three patch sets for PowerSTIG (described in my three other Issues) but one large blocker to me submitting proper PRs is that I'm not actually sure what the development/maintenance workflow for this repo is and how various modules link together to generated what is published on PSGallery. For those proposed patches, I have just been modifying offline modules that I downloaded via Powershell and have not played with any "Convert" module code.

Looking at previous PRs, it's unclear how updates for those STIGs are being converted/generated and what the process is for correcting translation errors. I suspect that the "Convert Wiki" linked in the README.md is supposed to house the bulk of this maintenance documentation, but that link is broken (as well as "StigData Wiki" mentioned in the next section).

I'm not sure what would be the full extent of good "maintainer documentation", but I would at least want the process for "setting up the build environment" and "updating the STIG specifications in PowerSTIG and correcting errors" to be documented. For documentation that allows someone new to take up some of the maintenance burden, I think the more the merrier :)

Thanks!

Start with README.md, especially the PowerStigConvert and PowerStigData sections and their broken wiki links. Trace the repository's described maintenance workflow for setting up the build environment, updating STIG specifications, and correcting translation errors. Done means a newcomer can follow the documented process for maintaining and publishing PowerSTIG modules.