It's behind the link in the post. On, perhaps, the worst git repo browser ever.
RMS's link: https://savannah.gnu.org/git/?group=c-intro-and-ref
click "browse sources repository" https://git.savannah.nongnu.org/cgit/c-intro-and-ref.git
hunt for the word "tree" and click it: https://git.savannah.nongnu.org/cgit/c-intro-and-ref.git/tre...
Oh look, a directory listing! Click the manual! https://git.savannah.nongnu.org/cgit/c-intro-and-ref.git/tre...
What, you don't want to read the 13k-line tex source? Sorry. Clone it and build it yourself, I guess.