GUIDE.md in rspreadsheet-0.3 vs GUIDE.md in rspreadsheet-0.4.1

- old
+ new

@@ -1,9 +1,9 @@
 ## Guide to basic functionality
 ### Opening the file
 
-You can open ODS file like this
+You can open ODS file (OpenDocument Spreadsheet) like this
 ````ruby
 @workbook = Rspreadsheet.open('./test.ods')
 ````
 and access its first sheet like this
 ````ruby
@@ -30,9 +30,17 @@
 
 ### Working with images
 @sheet.insert_image_to('10.21mm','15mm','image.png')
 i = @sheet.images.first
 i.move_to('100mm','99.98mm')
+
+### Saving 
+The file needs to be saved after doing changes. 
+````ruby
+@workbook.save
+@workbook.save('new_filename.ods')   # changes filename and saves
+@workbook.save(any_io_object)        # file can be saved to any IO like object as well
+````
 
 ## Examples
 
   * [basic functionality](https://gist.github.com/gorn/42e33d086d9b4fda10ec) 
   * [extended examples](https://gist.github.com/gorn/b432e6a69e82628349e6) of lots of alternative syntax