add support for image dependency diagram (docker images -viz)

.gitignore

@@ -8,3 +8,4 @@ lib/custom.bash
 plugins/custom.plugins.bash
 *.swp
 .*.un~
+/docker.png

aliases/available/docker.aliases.bash

@@ -8,6 +8,7 @@ alias dkpsa='docker ps -a'
 alias dki='docker images'
 alias dkrm='docker rm $(docker ps -a -q)'  # delete all stopped containers
 alias dkrmi='docker rmi $(docker images | grep "^<none>" | awk "{print $3}")'
+alias dkideps='docker images -viz | dot -Tpng -o docker.png && xdg-open docker.png ' # with graphviz
 
 # docker run [container] env
 function dkre() {