binary-search-tree: add hint to @Ignore tags

exercises/binary-search-tree/src/test/java/BSTTest.java

     }
 
     @Test
-    @Ignore
+    @Ignore("Remove to run test")
     public void insertsLess() {
         BST<Integer> sut = new BST();
         final int expectedRoot = 4;
     }
 
     @Test
-    @Ignore
+    @Ignore("Remove to run test")
     public void insertsSame() {
         BST<Integer> sut = new BST();
         final int expectedRoot = 4;
     }
 
     @Test
-    @Ignore
+    @Ignore("Remove to run test")
     public void insertsRight() {
         BST<Integer> sut = new BST();
         final int expectedRoot = 4;
     }
 
     @Test
-    @Ignore
+    @Ignore("Remove to run test")
     public void createsComplexTree() {
         BST<Integer> sut = new BST<>();
         List<Integer> expected = Collections.unmodifiableList(
     }
 
     @Test
-    @Ignore
+    @Ignore("Remove to run test")
     public void sortsSingleElement() {
         BST<Integer> sut = new BST<>();
         List<Integer> expected = Collections.unmodifiableList(
     }
 
     @Test
-    @Ignore
+    @Ignore("Remove to run test")
     public void sortsCollectionOfTwoIfSecondInsertedIsSmallerThanFirst() {
         BST<Integer> sut = new BST<>();
         List<Integer> expected = Collections.unmodifiableList(
     }
 
     @Test
-    @Ignore
+    @Ignore("Remove to run test")
     public void sortsCollectionOfTwoIfSecondInsertedIsBiggerThanFirst() {
         BST<Integer> sut = new BST<>();
         List<Integer> expected = Collections.unmodifiableList(
     }
 
     @Test
-    @Ignore
+    @Ignore("Remove to run test")
     public void iteratesOverComplexTree() {
         BST<Integer> sut = new BST<>();
         List<Integer> expected = Collections.unmodifiableList(