Add an example p4 trigger (#65)

examples/buildkite-trigger.sh

@@ -0,0 +1,29 @@
+#!/bin/bash
+set -euo pipefail
+
+
+# P4 Trigger script that triggers buildkite builds
+# Usage:
+# my-pipeline change-commit //depot/... "%//depot/scripts/buildkite-trigger.sh% <organisation> <pipeline> %changelist% %user% %email%"
+
+ORG_SLUG=$1
+PIPELINE_SLUG=$2
+
+CHANGELIST=$3
+USER=$4
+EMAIL=$5
+
+$(p4 -Ztag -F %desc% describe %3)
+
+PAYLOAD="{
+    \"commit\": \"@${CHANGELIST}\",
+    \"branch\": \"master\",
+    \"message\": \"${DESCRIPTION}\",
+    \"author\": {
+        \"name\": \"${USER}\",
+        \"email\": \"${EMAIL}\"
+    }
+}"
+
+curl -H "Authorization: Bearer $BUILDKITE_TOKEN" -X POST "https://api.buildkite.com/v2/organizations/${ORG_SLUG}/pipelines/${PIPELINE_SLUG}/builds" \
+  -d "${PAYLOAD}"