Added documentation for rbegin etc.

Author: 5cript

README.md

@@ -84,6 +84,10 @@ Creates an interval where the borders are sorted so the lower border is the firs
     - [iterator end()](#iterator-end)
     - [iterator cbegin()](#iterator-cbegin)
     - [iterator cend()](#iterator-cend)
+    - [iterator rbegin()](#iterator-rbegin)
+    - [iterator rend()](#iterator-rend)
+    - [iterator crbegin()](#iterator-crbegin)
+    - [iterator crend()](#iterator-crend)
 
 ### iterator insert(interval_type const& ival)
 Adds an interval into the tree. 
@@ -287,6 +291,32 @@ Returns a past the end const_iterator.
 
 ---
 
+---
+### iterator rbegin()
+Returns the iterator of the interval with the highest lower_bound.
+
+**Returns**: rbegin iterator.
+
+---
+### iterator rend()
+Returns a past the end iterator in reverse.
+
+**Returns**: past the end iterator.
+
+---
+### iterator crbegin()
+Returns the const_iterator of the interval with the highest lower_bound.
+
+**Returns**: begin iterator.
+
+---
+### iterator crend()
+Returns a past the end const_iterator in reverse.
+
+**Returns**: past the end const_iterator.
+
+---
+
 ## Members of Interval
 ___You can implement your own interval if you provide all the same functions.___