docs: add examples

examples/command_file.sh

@@ -0,0 +1,3 @@
+# This file is read from command_file.yaml
+# Go's text/teplate
+echo "{{.Task.Name}}"

examples/command_file.yaml

@@ -0,0 +1,7 @@
+---
+phases:
+- name: main
+  tasks:
+  - name: read command from a file
+    command:
+      command_file: command_file.sh

examples/main_test.go

@@ -16,6 +16,10 @@ func TestBuildflow(t *testing.T) { //nolint:funlen
 			title: "hello world",
 			file:  "hello_world.yaml",
 		},
+		{
+			title: "read command from a file (task.command_file)",
+			file:  "command_file.yaml",
+		},
 		{
 			title: "run tasks in parallel",
 			file:  "parallel.yaml",
@@ -25,8 +29,8 @@ 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.tengo

@@ -0,0 +1,5 @@
+// Tengo script
+// Define the variable "result" and this value should be true or false.
+result := func(task) {
+  return task.Name == "when"
+}(Task)

examples/task_when.yaml

@@ -0,0 +1,21 @@
+---
+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)
+  - name: read task.when from a file
+    command:
+      command: echo "hello"
+    when_file: task_when.tengo