docs updates

docs/objects/Checkbox/setSymbol.md

@@ -0,0 +1,18 @@
+## setSymbol
+Changes the checkbox symbol, default is "\42"
+
+#### Parameters: 
+1. `string` symbol
+
+#### Returns:
+1. `object` The object in use
+
+#### Usage:
+* Creates a new checkbox and changes the symbol to o
+```lua
+local main = basalt.createFrame()
+local checkbox = main:addCheckbox():setSymbol("o")
+```
+```xml
+<checkbox symbol="o" />
+```