This is a minimal example of how html lecture notes could be written in accessible way with bookdown. In principle also pdf and ebook can be produced, I just haven't touched that side much so far...
You'll need to install R, and then in R install bookdown by giving a command
install.packages('bookdown')
You will also need pandoc.
The conversion to html uses Makefile so you'll need "make"
It's possible to run it also without make, check the information on that, and on Bookdown in general, from the following (the text is copied from https://github.com/rstudio/bookdown-demo
This is a minimal example of a book based on R Markdown and bookdown (https://github.com/rstudio/bookdown). Please see the page "Get Started" at https://bookdown.org/yihui/bookdown/ for how to compile this example into HTML. You may generate a copy of the book in bookdown::pdf_book format by calling bookdown::render_book('index.Rmd', 'bookdown::pdf_book'). More detailed instructions are available here https://bookdown.org/yihui/bookdown/build-the-book.html.
You can find the preview of this example at https://bookdown.org/yihui/bookdown-demo/.
The make command converts the 01-text.tex file to 01-text.Rmd, from which the web pages are generated into the _book/ directory. Subsequent make commands only recreate the 01-text.Rmd if the tex file has been changed (with numbered backups created of the Rmd file).
To add more tex files, you'll need to add them to the OBJS line in the Makefile (delimited with a space). The files are collected in alphabetical order. If you write Rmd files directly, DON'T put them into the Makefile.
The 02-text.Rmd is an edited version of the 01-text.Rmd, with some other stuff...
The other files (yml, css, tex) control how the output looks like.