Add new highlight_duration config option to readme

Closes #5

README.md

@@ -31,7 +31,8 @@ Moving slowly, showing each command
 {
   "aaronik/treewalker.nvim",
   opts = {
-    highlight = true -- Whether to briefly highlight the node after jumping to it
+    highlight = true, -- Whether to briefly highlight the node after jumping to it
+    highlight_duration = 250, -- How long should above highlight last (in ms)
   }
 }
 ```