add workflow

Author: verchol

.github/main.workflow

@@ -0,0 +1,16 @@
+workflow "Apply PR labels" {
+  on = "pull_request"
+  resolves = "Apply labels"
+}
+
+action "On sync" {
+  uses = "actions/bin/filter@master"
+  args = "action synchronize"
+}
+
+action "Apply labels" {
+  uses = "actions/labeller@v1.0.0"
+  needs = "On sync"
+  env = {LABEL_SPEC_FILE=".github/triage.yml"}
+  secrets = ["GITHUB_TOKEN"]
+}