Quick Answer: Check out the 'Read-me'-Tab in the Worksheet with information on this quiestion.
Longer Answer: In most versions of Excel you can chose your favourite way to show comments which are added to a cell. GRI-citations are hidden in such comments. By default, cells which have a comment attached are marked with a red triangle at the upper right corner. Simply touch this triangle with the cursor, and the comment-box which holds the GRI-Text foldens up.