[tiomun]

Ok I figured it out.

<Bindings>
	<Layer name="|cFF8C00Rive|r Mouse Mod"> <--Must be "General"
		<Category name="General Options"><-- Must be to Addon name
			<Action name="RMM_MOUSE_MOD_ENABLE">
				<Down>RMM_ToggleEnabled()</Down>
			</Action>
		</Category>
	</Layer>
</Bindings>

So with the corrections

<Bindings>
	<Layer name="General">
		<Category name="|cFF8C00Rive|r Mouse Mod">
			<Action name="RMM_MOUSE_MOD_ENABLE">
				<Down>RMM_ToggleEnabled()</Down>
			</Action>
		</Category>
	</Layer>
</Bindings>

Which stinks! It looked cool having its own heading!