Treeview Docs

Added Treeview docs
Improved some stuff in the treeview object

docs/objects/Treeview/onSelect.md

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+## onSelect
+
+### Description
+
+`onSelect(self, node)`
+
+The `onSelect` event is triggered when a node in the Treeview object is clicked by the user. You can use this event to handle user interaction with the Treeview nodes.
+
+### Returns
+
+1. `object` The object in use
+
+### Usage
+
+* Creates a Treeview and handles the onSelect event:
+
+```lua
+local basalt = require("basalt")
+
+local mainFrame = basalt.createFrame()
+local treeview = mainFrame:addTreeview()
+
+local rootNode = treeview:getRoot()
+local childNode = rootNode:addChild("New Child")
+
+treeview:onSelect(function(self, node)
+    basalt.debug("Selected node:", node:getText())
+end)
+
+basalt.autoUpdate()
+```