test(playwright): move readme, add video tutorial (#4156)

tests/utils/screenShotPaths.ts

@@ -5,6 +5,9 @@ const screenShotPaths = {
   mpr: {
     mprDisplayedCorrectly: 'mprDisplayedCorrectly.png',
   },
+  length: {
+    lengthDisplayedCorrectly: 'lengthDisplayedCorrectly.png',
+  },
 };
 
 export { screenShotPaths };