ADD: insert type javadoc

src/mhtree/InsertType.java

 package mhtree;
 
+/**
+ * Specifies how should new objects be added to the MH-Tree.
+ */
 public enum InsertType {
+    /**
+     * When inserted object is not covered by node, all objects under such node are retrieved and a new hull is build,
+     * replacing the current one.
+     */
     GREEDY,
+
+    /**
+     * When inserted object is not overed by node, we iterate over hull objects beginning with the nearest hull object.
+     * We try to replace existing hull object by replacing current hull object by inserted object
+     * and checking if the replaced hull objects is covered by the new hull.
+     * This is repeated until such hull object is found or if not,
+     * the inserted object is simply added as a new hull object.
+     */
     INCREMENTAL,
 }