Welcome! Currently we have some limited initial documentation in the wiki (couple pages public so far) and try to comment the code well. I wrote an architecture page on how the new block loading system works, although that was before it got integrated and we did a package setup shuffle, so it already needs an update. We're right in the middle of some move/rename activity, after that's done we'll get back on more docs
begla could inform more on the optimization techniques, I think some are listed here and there in the dev forum threads, you might catch a few by looking around
Any thoughts on what specifically you'd like to contribute?