Improves hierarchy documentation (#7)

Author: aserebryakov

README.md

@@ -38,15 +38,20 @@ The sequence matching the expression '^\s\*[ ].\*' marks a line as a TODO list i
   [X] Done
 ```
 
-###### Items Hierarchy
+##### Items Hierarchy
+
+If one item has lesser indentation than the next one then the first one is meant
+to be **parent** and the second to be **child**.
+
+###### Example
 
 ```
   [ ] Parent
     [ ] Child1
     [ ] Child2
 ```
 
-Rules:
+###### Rules:
 * Changig state of the parent item changes the state of all children items accorndantly
 * If all children items are marked done, parent will also be marked as done
 * If parent is marked as done and one of the children changes state to not done

doc/vim-todo-lists.txt

@@ -62,6 +62,12 @@ Example
 Items Hierarchy
 ---------------
 
+If one item has lesser indentation than the next one then the first one is meant
+to be 'parent' and the second to be 'child'.
+
+Example
+-------
+
 [ ] Parent
   [ ] Child1
   [ ] Child2