Add Youtube link to javadoc

Author: andrei-punko

src/main/java/by/andd3dfx/string/StringTransformation.java

@@ -16,6 +16,8 @@
  * first = "ab", second = "ba" -> false
  * first = "abcd", second = "abd" -> true
  * </pre>
+ *
+ * @see <a href="https://youtu.be/GOSWr4jHng8">Video solution</a>
  */
 public class StringTransformation {