minesweeper: add hints to @Ignore annotations

exercises/minesweeper/src/test/java/MinesweeperBoardTest.java

         assertEquals(expectedAnnotatedRepresentation, actualAnnotatedRepresentation);
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testInputBoardWithOneRowAndNoColumns() {
         final List<String> inputBoard = Collections.singletonList("");
         assertEquals(expectedAnnotatedRepresentation, actualAnnotatedRepresentation);
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testInputBoardWithNoMines() {
         final List<String> inputBoard = Arrays.asList(
         assertEquals(expectedAnnotatedRepresentation, actualAnnotatedRepresentation);
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testInputBoardWithOnlyMines() {
         final List<String> inputBoard = Arrays.asList(
         assertEquals(expectedAnnotatedRepresentation, actualAnnotatedRepresentation);
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testInputBoardWithSingleMineAtCenter() {
         final List<String> inputBoard = Arrays.asList(
         assertEquals(expectedAnnotatedRepresentation, actualAnnotatedRepresentation);
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testInputBoardWithMinesAroundPerimeter() {
         final List<String> inputBoard = Arrays.asList(
         assertEquals(expectedAnnotatedRepresentation, actualAnnotatedRepresentation);
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testInputBoardWithSingleRowAndTwoMines() {
         final List<String> inputBoard = Collections.singletonList(
         assertEquals(expectedAnnotatedRepresentation, actualAnnotatedRepresentation);
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testInputBoardWithSingleRowAndTwoMinesAtEdges() {
         final List<String> inputBoard = Collections.singletonList(
         assertEquals(expectedAnnotatedRepresentation, actualAnnotatedRepresentation);
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testInputBoardWithSingleColumnAndTwoMines() {
         final List<String> inputBoard = Arrays.asList(
         assertEquals(expectedAnnotatedRepresentation, actualAnnotatedRepresentation);
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testInputBoardWithSingleColumnAndTwoMinesAtEdges() {
         final List<String> inputBoard = Arrays.asList(
         assertEquals(expectedAnnotatedRepresentation, actualAnnotatedRepresentation);
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testInputBoardWithMinesInCross() {
         final List<String> inputBoard = Arrays.asList(
         assertEquals(expectedAnnotatedRepresentation, actualAnnotatedRepresentation);
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testLargeInputBoard() {
         final List<String> inputBoard = Arrays.asList(
         assertEquals(expectedAnnotatedRepresentation, actualAnnotatedRepresentation);
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testNullInputBoardIsRejected() {
         expectedException.expect(IllegalArgumentException.class);
         new MinesweeperBoard(null);
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testInputBoardWithInvalidSymbolsIsRejected() {
         expectedException.expect(IllegalArgumentException.class);
         new MinesweeperBoard(Collections.singletonList(" * & "));
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testInputBoardWithInconsistentRowLengthsIsRejected() {
         expectedException.expect(IllegalArgumentException.class);