This is useful in particular for repositories which explains some concepts on bunch of markdown files, in order to decrease back, forth navigation. A single PDF file can be generated through following steps:
$ for file in $(find . -name "*.md" | sort); do echo -e "\n\n# $(basename "$file" .md)\n\n" >> combined.md; cat "$file" >> combined.md; done
$ pandoc combined.md -o Grokking_System_Design.pdf