Some docs updates

docs/objects/Scrollbar/setIndex.md

@@ -0,0 +1,21 @@
+## setIndex
+Changes the current index to your choice, for example you could create a button which scrolls up to 1 by using :setIndex(1)
+
+#### Parameters: 
+1. `number` the index
+
+#### Returns:
+1. `object` The object in use
+
+#### Usage:
+* Creates a new scrollbar and changes the index to 1 as soon as the button got clicked
+```lua
+local main = basalt.createFrame()
+local scrollbar = main:addScrollbar():setMaxValue(20)
+local button = main:addButton(function()
+    scrollbar:setIndex(1)
+end)
+```
+```xml
+<scrollbar index="2" />
+```