Add defaultIsVisible to walkthrough docs

Author: rickhanlonii

docs/Walkthrough.md

@@ -45,8 +45,10 @@ const DevTools = createDevTools(
   // Monitors are individually adjustable with props.
   // Consult their repositories to learn about those props.
   // Here, we put LogMonitor inside a DockMonitor.
+  // Note: DockMonitor is visible by default.
   <DockMonitor toggleVisibilityKey='ctrl-h'
-               changePositionKey='ctrl-q'>
+               changePositionKey='ctrl-q'
+               defaultIsVisible={true}>
     <LogMonitor theme='tomorrow' />
   </DockMonitor>
 );