'Revision History' on documents can be found in the context menu under the Inspects and Views option:

If you are using the new Context Mode the revision history will be found here:

Enter on the 'revision history' and changes made to the document/item will be listed.

If no changes are logged, there will not be an options for revision history. 

If you are using the new context menu - the selection will be gray with a message stating no revisions to show:


Nb: The 'new' context menu can be activated under your user profile.