[clang-tools-extra] [clang-doc][NFC] Add TODO for future work (PR #138052)

[Petr Hosek via cfe-commits]

================
@@ -60,6 +60,7 @@ struct CommentInfo {
   // the vector.
   bool operator<(const CommentInfo &Other) const;
 
+  // TODO: The Kind field should be an enum, so we can switch on it easily
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petrhosek wrote:

```suggestion
  // TODO: The Kind field should be an enum, so we can switch on it easily.
```

https://github.com/llvm/llvm-project/pull/138052