Rename "intro" to "high-level" and "internals" to "low-level"

levels/low-level/welcome

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+[description]
+
+This is prototype #1 for the Git learning game by @bleeptrack and @blinry. Thanks for checking it out! <3
+
+You can interact with the repository on the right by typing Bash commands in the terminal below! The visualization will show you its internal status.
+
+Let's get started by initializing an empty Git repository in the current directory by typing:
+
+    git init
+
+[congrats]
+
+Well done!
+
+An empty Git repository is... well, quite empty. The only thing that always exists is a reference called "HEAD" - we'll learn what that is later!
+
+But first, let's look at some basics!
+
+(Click "Next Level" as soon as you're ready!)
+
+[setup]
+
+rm -rf .git
+
+[setup goal]
+
+rm -rf .git
+
+git init
+
+[win]
+
+test -d .git