Treeview Docs

Added Treeview docs
Improved some stuff in the treeview object

docs/objects/Treeview/addChild.md

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+## addChild
+
+### Description
+
+The `addChild` method adds a new child node to a specified node within a Treeview object.
+
+### Parameters
+
+1. `string` The text of the new child node.
+2. `boolean` Whetever the child node is expandable
+
+### Returns
+
+1. `node` The newly created child node
+
+### Usage
+
+* Creates a Treeview, adds a child node to the root node:
+
+```lua
+local basalt = require("basalt")
+
+local mainFrame = basalt.createFrame()
+local treeview = mainFrame:addTreeview()
+
+local rootNode = treeview:getRoot()
+local childNode = rootNode.addChild("Child Node")
+
+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.