[clang] Revise the modules document for clarity (PR #90237)

[Vlad Serebrennikov via cfe-commits]

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@@ -279,8 +266,9 @@ we could put ``-x c++-module`` in front of the file. For example,
     return 0;
   }
 
-Now the filename of the ``module interface`` ends with ``.cpp`` instead of ``.cppm``,
-we can't compile them by the original command lines. But we are still able to do it by:
+In this example, the extension used by the ``module interface`` is ``.cpp``
+instead of ``.cppm``, so is cannot be compiled with the command lines from the
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Endilll wrote:

```suggestion
instead of ``.cppm``, so it cannot be compiled with the command lines from the
```

https://github.com/llvm/llvm-project/pull/90237