move files to repo's root

.gitignore

README.md

build.ninja

default.nix

fig/00-parent-begin.svg

fig/01-parent-pipe.svg

fig/02-parent-fork.svg

fig/03-parent-fork-focus-pipe.svg

fig/04-parent-switch.svg

fig/05-parent-close.svg

fig/06-parent-close-done.svg

fig/07-parent-read-blocked.svg

fig/08-child-switch.svg

fig/09-child-close.svg

fig/10-child-close-done.svg

fig/11-child-dup2.svg

fig/12-child-dup2-done.svg

fig/13-child-dup2-done2.svg

fig/14-child-exec.svg

fig/15-child-exec-done.svg