Thanks @BigEd, both for the github pages info and the changes to readme.md (which I shamelessly copied (save for swapping intro & summary/contents to match @lawrie's book) - I was planning on asking you to open a pull request, but wanted to see the change ... I did credit you in the commit message - hope that is ok)
For now I've selected the Leap Day theme - I'm not keen on the yellow stripe but the tables looked quite neat and the page navigation (if the screen width is wide enough) looked interesting. It misses some of the hardware headers off as the section is quite long - I'm thinking that if I can understand something more about the theme it might be possible to get a better navigation side panel (e.g. something between pages and working on mobiles / sub full HD screens).
See what you think at https://piersh.github.io/opensourcefpgas/ - Easy to change if we want to
Well spotted @BigEd - Gitbook seams to struggle with the order of the chapters. I don't know why ...
I'm not sure what gitbooks is offering - the legacy version did offer conversion to pdf