DOC: Make wording in absolute beginners guide more friendly (numpy#27788)

Author: StanFromIreland

doc/source/user/absolute_beginners.rst

@@ -664,7 +664,10 @@ where you want to slice your array. ::
   array([4, 5, 6, 7, 8])
 
 Here, you grabbed a section of your array from index position 3 through index
-position 8.
+position 8 but not including position 8 itself.
+
+*Reminder: Array indexes begin at 0. This means the first element of the array is at index 0,
+the second element is at index 1, and so on.*
 
 You can also stack two existing arrays, both vertically and horizontally. Let's
 say you have two arrays, ``a1`` and ``a2``::