Documentation: document image lifecycle and implementation.
Documentation: document image lifecycle and implementation.

Document the image lifecycle phases, their logic and explain the rkt implementations.

joshix/rkt,Wilybald/rkt,joshix/rkt,cab105/rkt,lucasallan/rkt,s-urbaniak/rkt,ybubnov/rkt,jakon89/rkt,intelsdi-x/rkt,coreos/rkt,shobhit85/rkt,rkt/rkt,alban/rkt,yifan-gu/rocket,s-urbaniak/rkt,yifan-gu/rocket,cab105/rkt,sstabellini/rkt,jonboulle/rkt,jakon89/rkt,yifan-gu/rocket,joshix/rkt,joshix/rkt,lucasallan/rkt,intelsdi-x/rkt,sstabellini/rkt,squeed/rkt,shobhit85/rkt,yifan-gu/rkt,dgonyeo/rkt,Shashwatsh/rkt,squeed/rkt,Shashwatsh/rkt,lucasallan/rkt,squeed/rkt,coreos/rkt,jonboulle/rkt,Wilybald/rkt,rkt/rkt,achanda/rkt,Shashwatsh/rkt,dgonyeo/rkt,euank/rkt,lucasallan/rkt,kinvolk/rkt,yifan-gu/rkt,intelsdi-x/rkt,Wilybald/rkt,rkt/rkt,kinvolk/rkt,coreos/rkt,nhlfr/rkt,rkt/rkt,achanda/rkt,euank/rkt,jonboulle/rkt,yifan-gu/rkt,alban/rkt,jakon89/rkt,kinvolk/rkt,ybubnov/rkt,sstabellini/rkt,kinvolk/rkt,s-urbaniak/rkt,euank/rkt,alban/rkt,cab105/rkt,ybubnov/rkt,Wilybald/rkt,achanda/rkt,nhlfr/rkt,nhlfr/rkt,shobhit85/rkt,dgonyeo/rkt