To distribute them in tarballs.
- autogen.sh: could be useful, but it's normally ./configure that needs
  to be executed. In any case, it doesn't hurt to include autogen.sh (I
  think it could be useful for MSYS2 packaging, so for Windows).
- README.md: this is of course important.

What's still missing, and I don't really know:
- git.mk: not distributed in tarballs, but of course this is for Git
  purposes, not for tarballs. So I guess it's fine.