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

[Erich Keane via cfe-commits]

================
@@ -216,51 +198,56 @@ We explain the options in the following sections.
 How to enable standard C++ modules
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-Currently, standard C++ modules are enabled automatically
-if the language standard is ``-std=c++20`` or newer.
+Standard C++ modules are enabled automatically if the language standard is
+``-std=c++20`` or newer.
 
 How to produce a BMI
 ~~~~~~~~~~~~~~~~~~~~
 
-We can generate a BMI for an importable module unit by either ``--precompile``
-or ``-fmodule-output`` flags.
+To generate a BMI for an importable module unit, use either the ``--precompile``
+or ``-fmodule-output`` command line option.
----------------
erichkeane wrote:

```suggestion
or ``-fmodule-output`` command line options.
```

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