Polish levels some more, add a "congrats" text

levels/basics/congrats

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+Omnomnom!
+
+For technical reasons, you can't use `cd` in this prototype yet. But there won't be a lot of interaction with the file system anyways. :)

levels/basics/description

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+For this prototype, we assume you have some experience with the command line. Here are some commands that will be useful:
+
+- ls
+- echo content > file
+- cat file
+- mkdir dir
+
+Find the riddle in your current directory and put the answer into the file "answer"!

levels/basics/start

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+mkdir riddle
+echo "ppl p" > riddle/consonants
+echo "ae ie" > riddle/vowels

levels/basics/win

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+cat answer | grep -i "apple \\?pie"