refine docs for ctrl key (#5831)

Author: fatadel

docs-user/guide-ui-tour-panels.md

@@ -6,7 +6,9 @@ Get to know Firefox Profiler UI a bit better with a tour that highlights various
 
 ![A screenshot highlighting the panels on the lower half of the UI.](images/ui-tour-panels.png)
 
-The timeline lists multiple threads, while the panels provide an analysis of the currently selected thread in the timeline. The panel only uses one thread at a time by default. However it's possible to merge several threads together by using the `Ctrl` keyboard key when clicking a thread.
+The timeline lists multiple threads, while the panels provide an analysis of the currently selected thread in the timeline.
+The panel only uses one thread at a time by default.
+However, it's possible to merge several threads together by using the `⌘`/`Ctrl` keyboard key when clicking a thread.
 
 ## The Call Tree