Add an example about files order

Author: nbirillo

.courseignore

@@ -1 +1,2 @@
-README.md
+README.md
+/.run

README.md

@@ -155,6 +155,7 @@ It provides the list of files or directories that will be ignored in the final c
 
 ```text
 README.md
+/.run
 ```
 
 You can find more information about the course preview in the [Course preview][ref:course.preview] section. Information 

common/src/main/resources/images/files-order.gif

@@ -3,3 +3,4 @@ content:
   - theoryTask
   - quizTask
   - programmingTask
+  - multiFileTask

courseSection/courseLesson/lesson-info.yaml

@@ -0,0 +1,3 @@
+fun main() {
+    helloWorld()
+}

courseSection/courseLesson/multiFileTask/src/Main.kt

@@ -0,0 +1 @@
+fun helloWorld(): Unit = println("Hello, world!")

courseSection/courseLesson/multiFileTask/src/MainTaskFile.kt

@@ -0,0 +1,18 @@
+type: output
+files:
+  - name: src/MainTaskFile.kt
+    visible: true
+    placeholders:
+      - offset: 25
+        length: 24
+        placeholder_text: TODO("Not implemented yet")
+  - name: src/Main.kt
+    visible: true
+    placeholders:
+      - offset: 17
+        length: 12
+        placeholder_text: // invoke the implemented functions here
+  - name: test/output.txt
+    visible: false
+  - name: test/input.txt
+    visible: false

courseSection/courseLesson/multiFileTask/task-info.yaml

@@ -0,0 +1,8 @@
+This is an example of an input/output task. 
+In this type of task, you can give an expected input and output to the program instead of implementing 
+your own tests.
+
+This task also demonstrates how you can set up which file should be opened in the student mode if the task has several files.
+You just need to put this file as the first file in the `task-info.yaml` config, e.g. in this task the `MainTaskFile.kt` will be opened: 
+
+![Expected behaviour](../../../common/src/main/resources/images/files-order.gif)

courseSection/courseLesson/multiFileTask/task.md

@@ -0,0 +1 @@
+Hello, world!