[docs] note that some exercise currently don't work

Related to #124 and #125

Author: dummdidumm

Diff for: content/tutorial/01-svelte/06-bindings/05-textarea-inputs/README.md

@@ -2,6 +2,8 @@
 title: Textarea inputs
 ---
 
+> This exercise doesn't currently work. You can switch to the old tutorial instead: https://svelte.dev/tutorial/textarea-inputs
+
 The `<textarea>` element behaves similarly to a text input in Svelte — use `bind:value`:
 
 ```svelte

Diff for: content/tutorial/01-svelte/07-lifecycle/01-onmount/README.md

@@ -2,6 +2,8 @@
 title: onMount
 ---
 
+> The images in this exercise don't currently work. You can switch to the old tutorial instead: https://svelte.dev/tutorial/onmount
+
 Every component has a _lifecycle_ that starts when it is created, and ends when it is destroyed. There are a handful of functions that allow you to run code at key moments during that lifecycle.
 
 The one you'll use most frequently is `onMount`, which runs after the component is first rendered to the DOM.

Diff for: content/tutorial/03-advanced-svelte/05-bindings/03-media-elements/README.md

@@ -2,6 +2,8 @@
 title: Media elements
 ---
 
+> This exercise doesn't currently work. You can switch to the old tutorial instead: https://svelte.dev/tutorial/media-elements
+
 The `<audio>` and `<video>` elements have several properties that you can bind to. This example demonstrates a few of them.
 
 On line 62, add `currentTime={time}`, `duration` and `paused` bindings:

Diff for: content/tutorial/03-advanced-svelte/07-composition/04-optional-slots/README.md

@@ -2,6 +2,8 @@
 title: Checking for slot content
 ---
 
+> The images in this exercise don't currently work. You can switch to the old tutorial instead: https://svelte.dev/tutorial/optional-slots
+
 In some cases, you may want to control parts of your component based on whether the parent passes in content for a certain slot. Perhaps you have a wrapper around that slot, and you don't want to render it if the slot is empty. Or perhaps you'd like to apply a class only if the slot is present. You can do this by checking the properties of the special `$$slots` variable.
 
 `$$slots` is an object whose keys are the names of the slots passed in by the parent component. If the parent leaves a slot empty, then `$$slots` will not have an entry for that slot.

Diff for: content/tutorial/03-advanced-svelte/08-context/01-context-api/README.md

@@ -2,6 +2,8 @@
 title: setContext and getContext
 ---
 
+> This exercise doesn't currently work. You can switch to the old tutorial instead: https://svelte.dev/tutorial/context-api
+
 The context API provides a mechanism for components to 'talk' to each other without passing around data and functions as props, or dispatching lots of events. It's an advanced feature, but a useful one.
 
 Take this example app using a [Mapbox GL](https://docs.mapbox.com/mapbox-gl-js/overview/) map. We'd like to display the markers, using the `<MapMarker>` component, but we don't want to have to pass around a reference to the underlying Mapbox instance as a prop on each component.