Add keyboard shortcut for holding shift to see additional time format…

…s in the timeline tooltip

docs/keyboard-shortcuts.mdx

@@ -30,6 +30,7 @@ The easiest way to navigate the timeline is by holding <Shortcut>⌘</Shortcut>
 - <Shortcut>ctrl</Shortcut> + <Shortcut>T</Shortcut> toggles the cursor visibility
 - <Shortcut>0</Shortcut> resets the timeline zoom
 - <Shortcut>delete</Shortcut> or <Shortcut>backspace</Shortcut> deletes selected activity directive
+- <Shortcut>shift</Shortcut> when held shows additional time formats within the timeline tooltip
 
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