Sync the anagram exercise's docs with the latest data. (#991)

exercises/practice/anagram/.docs/instructions.md

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 # Instructions
 
-An anagram is a rearrangement of letters to form a new word: for example `"owns"` is an anagram of `"snow"`.
-A word is not its own anagram: for example, `"stop"` is not an anagram of `"stop"`.
+Your task is to, given a target word and a set of candidate words, to find the subset of the candidates that are anagrams of the target.
 
-Given a target word and a set of candidate words, this exercise requests the anagram set: the subset of the candidates that are anagrams of the target.
+An anagram is a rearrangement of letters to form a new word: for example `"owns"` is an anagram of `"snow"`.
+A word is _not_ its own anagram: for example, `"stop"` is not an anagram of `"stop"`.
 
 The target and candidates are words of one or more ASCII alphabetic characters (`A`-`Z` and `a`-`z`).
 Lowercase and uppercase characters are equivalent: for example, `"PoTS"` is an anagram of `"sTOp"`, but `StoP` is not an anagram of `sTOp`.

exercises/practice/anagram/.docs/introduction.md

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+# Introduction
+
+At a garage sale, you find a lovely vintage typewriter at a bargain price!
+Excitedly, you rush home, insert a sheet of paper, and start typing away.
+However, your excitement wanes when you examine the output: all words are garbled!
+For example, it prints "stop" instead of "post" and "least" instead of "stale."
+Carefully, you try again, but now it prints "spot" and "slate."
+After some experimentation, you find there is a random delay before each letter is printed, which messes up the order.
+You now understand why they sold it for so little money!
+
+You realize this quirk allows you to generate anagrams, which are words formed by rearranging the letters of another word.
+Pleased with your finding, you spend the rest of the day generating hundreds of anagrams.