Perhaps this basic guide will be helpful  

The building sections is copied from one of the old design docs; tbh i was mainly focused on doing the units and bonuses.   They will probably need rams purely for gameplay reasons (it was decide a while ago that all civs will have them iirc). I suppose they could extrapolate from later rams or use the log ram as with the Germans. https://research.vu.nl/ws/files/42190004/chapter 10.pdf The actual archaic siege methods would be a bit hard to portray through gameplay (although a tech or passive bonus that makes infantry stronger against buildings to somewhat compensate for poor siege is possible)

New Version, now with a button "Check for Updates" on the mod selection screen prior to downloading anything ewlse (thanks to @Asher) . Unfortunately, for me everything is green as my mods are all updated already... Could somebode please do some testing? Again R28 is for Version 0.28 and R29 for the new SVN version 0.29 (nightly build). There is also a little user and maintainer documentation. modiomod-changes.md modiomod-r28.zip modiomod-r29.zip

So, how do I make a PR, do I need to be added to a list of editors for the repo?

Ok, got it working!