Treeview Docs

Added Treeview docs
Improved some stuff in the treeview object

docs/objects/Treeview/onSelectNode.md

@@ -0,0 +1,36 @@
+## onSelect
+
+### Description
+
+The `onSelect` event is triggered when a node within a Treeview object is clicked or selected by the user. This event allows you to define custom behavior or actions that should be executed when the node is selected.
+
+### Parameters
+
+1. `function` The callback function that will be executed when the node is selected. This function receives one argument:
+    * `node`: The node that was selected.
+
+### Returns
+
+1. `node` The node in use
+
+### Usage
+
+* Creates a Treeview, adds a child node to the root node, and checks if the root node is expanded:
+
+```lua
+local basalt = require("basalt")
+
+local mainFrame = basalt.createFrame()
+local treeview = mainFrame:addTreeview()
+
+local rootNode = treeview:getRoot()
+local childNode = rootNode.addChild("Child Node")
+
+childNode.onSelect(function(node)
+  basalt.debug("Node selected:", node.getText())
+end)
+
+basalt.autoUpdate()
+```
+
+In this example, a Treeview object is created and added to the mainFrame. The `getRoot` method is used to access the root node, and a new child node is added to it using the `addChild` method. The `onSelect` event is then assigned to the child node with a callback function that will display the text of the selected node using `basalt.debug` when the node is clicked or selected.