add: action

.github/main.workflow

@@ -0,0 +1,9 @@
+workflow "Main workflow" {
+  on = "push"
+  resolves = ["docker-build"]
+}
+
+action "docker-build" {
+  uses = "actions/docker/cli@master"
+  args = "build -t peaceiris/actions-hugo ."
+}