docs: add an example

examples/main_test.go

@@ -25,8 +25,8 @@ func TestBuildflow(t *testing.T) { //nolint:funlen
 			file:  "task_dependency.yaml",
 		},
 		{
-			title: "task.when is true",
-			file:  "task_when_true.yaml",
+			title: "task.when",
+			file:  "task_when.yaml",
 		},
 		{
 			title: "read_file",

examples/task_when.yaml

@@ -0,0 +1,17 @@
+---
+phases:
+- name: main
+  tasks:
+  - name: "when true"
+    command:
+      command: echo "when is always true"
+    when: true
+  - name: when
+    command:
+      command: echo "use Tengo script in when"
+    when: |
+      // Tengo script
+      // Define the variable "result" and this value should be true or false.
+      result := func(task) {
+        return task.Name == "when"
+      }(Task)