rectangles: add hint to @Ignore annotations

exercises/rectangles/src/test/java/RectangleCounterTest.java

         assertEquals(0, rectangleCounter.countRectangles(inputGrid));
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testNonTrivialInputWithNoRectangles() {
         String[] inputGrid = new String[]{" "};
         assertEquals(0, rectangleCounter.countRectangles(inputGrid));
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testInputWithOneRectangle() {
         String[] inputGrid = new String[]{
         assertEquals(1, rectangleCounter.countRectangles(inputGrid));
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testInputWithTwoRectanglesWithoutSharedEdges() {
         String[] inputGrid = new String[]{
         assertEquals(2, rectangleCounter.countRectangles(inputGrid));
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testInputWithFiveRectanglesWithSharedEdges() {
         String[] inputGrid = new String[]{
         assertEquals(5, rectangleCounter.countRectangles(inputGrid));
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testThatRectangleOfHeightOneIsCounted() {
         String[] inputGrid = new String[]{
         assertEquals(1, rectangleCounter.countRectangles(inputGrid));
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testThatRectangleOfWidthOneIsCounted() {
         String[] inputGrid = new String[]{
         assertEquals(1, rectangleCounter.countRectangles(inputGrid));
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testThatOneByOneSquareIsCounted() {
         String[] inputGrid = new String[]{
         assertEquals(1, rectangleCounter.countRectangles(inputGrid));
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testThatIncompleteRectanglesAreNotCounted() {
         String[] inputGrid = new String[]{
         assertEquals(1, rectangleCounter.countRectangles(inputGrid));
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testThatRectanglesOfDifferentSizesAreAllCounted() {
         String[] inputGrid = new String[]{
         assertEquals(3, rectangleCounter.countRectangles(inputGrid));
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testThatIntersectionsWithoutCornerCharacterDoNotCountAsRectangleCorners() {
         String[] inputGrid = new String[]{
         assertEquals(2, rectangleCounter.countRectangles(inputGrid));
     }
 
-    @Ignore
+    @Ignore("Remove to run test")
     @Test
     public void testLargeInputWithManyRectangles() {
         String[] inputGrid = new String[]{