It seems that Dennis Ritchie wrote a paper 'A Tour through the Unix C
Compiler' which is quite useful in understanding the compiler. I have
converted the doc to Markdown format as well which makes it easier to
read.
You might try downloading the PDF or PS versions of the V7 documents from amazon. It seems like a lot less work work and will be a lot easier to read. Also Gnu groff runs on pretty much everything these days, so going from the V7 troff sources yourself is not difficult; in fact its pretty smart. Its still the best 'pure document compiler' out there. And it means you can add your additions/ corrections / notes to what Dennis did right inline.