Update docs

docs/tut/crash-course/8-cleanup.md

@@ -1,48 +0,0 @@
-# Cleanup
-
-Sometimes you may need to do some cleanup when destroying a component or after
-a side-effect from a source update. Vide provides a function `cleanup()` which
-is used to register a cleanup callback for the next time the reactive scope
-it is called in re-runs.
-
-```lua
-locla mount = vide.mount
-local source = vide.source
-local cleanup = vide.cleanup
-
-local function Timer()
-    local count = source(0)
-
-    local con = game:GetService("RunService").Heartbeat:Connect(function(dt)
-        count(count() + dt)
-    end)
-
-    cleanup(function()
-        con:Disconnect()
-    end)
-
-    return create "TextButton" {
-        Position = UDim2.fromOffset(300, 300),
-        Size = UDim2.fromOffset(200, 50),
-
-        Text = function()
-            return "seconds: " .. math.floor(count())
-        end,
-    }
-end
-
-local unmount = mount(Timer)
-
-unmount() -- all registered cleanups are ran, heartbeat connection stopped
-```
-
-In the above example, this allows us to disconnect the heartbeat connection
-when the timer component is destroyed, whether that is from unmounting the app
-or if it is dynamically created by a control-flow function, which will be
-covered next.
-
-On a related note: the reason why `mount()` is used to create your app, is so
-that any top-level components that need to be cleaned up, can be cleaned up
-when the app is later unmounted, since `mount()` runs in a reactive scope to
-track `cleanup()` calls. Vide's entire reactive system is independent from the
-life-time of instances; instances are just a side-effect of the reactive system.