DOC: Clarify plot_topo interactivity (#14091)

Co-authored-by: Daniel McCloy <dan@mccloy.info>

Author: mh105

tutorials/raw/40_visualize_raw.py

@@ -156,7 +156,8 @@
 spectrum.plot_topo()
 
 # %%
-# This plot is also interactive; hovering over each "thumbnail" plot will
+# This plot is also interactive if an interactive backend is enabled; hovering
+# over each "thumbnail" plot will
 # display the channel name in the bottom left of the plot window, and clicking
 # on a thumbnail plot will create a second figure showing a larger version of
 # the selected channel's spectral density (as if you had called