Add note about width, height directives in Ex5

Author: sarina

Exercise 5/README.rst

@@ -5,8 +5,16 @@ Your task is to match this output (note! the horizontal line is drawn by GitHub
 
 .. image:: Match_This_Output.png
 
+Tip
+***
 
-Do so by clicking on `Exercise5.rst <https://github.com/sarina/rst-tutorial/blob/main/Exercise%205/Exercise5.rst>`_,
+To scale an image, you can add a ``:width:`` or ``:height:`` directive to cap
+the width or height of an image to a certain number of pixels.
+
+Completing the Exercise
+***********************
+
+Complete the exercise by clicking on `Exercise5.rst <https://github.com/sarina/rst-tutorial/blob/main/Exercise%205/Exercise5.rst>`_,
 clicking the pencil icon to edit, then editing the text with your own RST.
 Use the Preview tab to check out how you're doing; you can click back to
 "Edit File" as many times as you want to adjust your text.