Improved the wording for 'Summary 1 ex 10' description

based on https://github.com/BruceEckel/AtomicKotlinExamples/issues/20

Programming Basics/Summary 1/Exercise 10/src/Task.kt

@@ -17,9 +17,14 @@ fun showSnake(rows: Int, columns: Int) {
 }
 
 fun main() {
+  showSnake(2, 3)
+  println()
   showSnake(4, 5)
 }
 /* Output:
+ 0 1 2
+ 5 4 3
+
   0  1  2  3  4
   9  8  7  6  5
  10 11 12 13 14

Programming Basics/Summary 1/Exercise 10/task.md

@@ -10,5 +10,15 @@ filled with sequential numbers in a form of snake. For example, `showSnake(3,
  6 7 8
 ```
 
-For proper alignment, use `"%3d".format(number)` to place any necessary spaces
-before the number.
+For proper alignment, use a format string such as `"%3d".format(number)` to
+place additional spaces before the number. The number before `d` indicates how
+many characters the number should occupy together with the additional spaces.
+It depends on the biggest number, the last one: put exactly one space before it.
+
+<div class="hint">
+
+Use the string `"%${width}d".format(value)`, where the `width` variable stores
+the width of each number cell, to format the value based on the actual input
+(`rows` and `columns`). 
+
+</div>

Programming Basics/Summary 1/Exercise 10/test/Tests.kt

@@ -10,7 +10,8 @@ import util.runAndCheckSystemOutput
 class TestSummaryIExercise10 {
   private fun checkOutput(rows: Int, columns: Int, expected: String) {
     runAndCheckSystemOutput(
-      "Incorrect output for rows = $rows, columns = $columns:",
+      "Incorrect output for rows = $rows, columns = $columns " +
+        "(pay attention to the spaces!):",
       expected) {
       showSnake(rows, columns)
     }