Add docs for Buffer.lastIndexOf

doc/api/buffer.markdown

@@ -593,6 +593,46 @@ for (var key of buf.keys()) {
 //   5
 ```
 
+### buf.lastIndexOf(value[, byteOffset][, encoding])
+
+* `value` {String|Buffer|Number}
+* `byteOffset` {Number} Default: `buf.length`
+* `encoding` {String} Default: `'utf8'`
+* Return: {Number}
+
+Identical to [`Buffer#indexOf()`][], but searches the Buffer from back to front
+instead of front to back. Returns the starting index position of `value` in
+Buffer or `-1` if the Buffer does not contain `value`. The `value` can be a
+String, Buffer or Number. Strings are by default interpreted as UTF8. If
+`byteOffset` is provided, will return the last match that begins at or before
+`byteOffset`.
+
+```js
+const buf = new Buffer('this buffer is a buffer');
+
+buf.lastIndexOf('this');
+  // returns 0
+buf.lastIndexOf('buffer');
+  // returns 17
+buf.lastIndexOf(new Buffer('buffer'));
+  // returns 17
+buf.lastIndexOf(97); // ascii for 'a'
+  // returns 15
+buf.lastIndexOf(new Buffer('yolo'));
+  // returns -1
+buf.lastIndexOf('buffer', 5)
+  // returns 5
+buf.lastIndexOf('buffer', 4)
+  // returns -1
+
+const utf16Buffer = new Buffer('\u039a\u0391\u03a3\u03a3\u0395', 'ucs2');
+
+utf16Buffer.lastIndexOf('\u03a3', null, 'ucs2');
+  // returns 6
+utf16Buffer.lastIndexOf('\u03a3', -5, 'ucs2');
+  // returns 4
+```
+
 ### buf.length
 
 * {Number}