Add sandbox button to the title, and add CLI badge explainer

levels/sandbox/empty

@@ -1,3 +1,7 @@
 title = Empty sandbox
 
+[description]
+
+This is an empty sandbox you can play around in.
+
 [setup]

levels/sandbox/sequence

@@ -0,0 +1,2 @@
+empty
+three-commits

levels/sandbox/three-commits

@@ -1,4 +1,5 @@
-title = Three commits
+title = Sandbox
+cards = checkout add reset-file checkout-file commit merge rebase
 
 [setup]
 
@@ -16,9 +17,9 @@ git branch not_main
 
 [description]
 
-That's all for now! Here's a sandbox you can play around in.
+Here's a sandbox you can play around in.
 
-Did you see the black terminal at the very bottom? All cards you play translate into actual commands, and there'a a real Git repo behind this! Fun things to try:
+You can use both the playing cards, as well as the terminal. Fun things to try:
 
 - Make a commit that merges three timelines together at once!
 - Create some tags!