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

[Vlad Serebrennikov via cfe-commits]

================
@@ -925,45 +923,41 @@ In that case, you need to convert your source files (.cpp files) to module imple
   // Following off should be unchanged.
   ...
 
-The module implementation unit will import the primary module implicitly.
-We don't include any headers in the module implementation units
-here since we want to avoid duplicated declarations between translation units.
-This is the reason why we add non-exported using declarations from the third
-party libraries in the primary module interface unit.
+The module implementation unit will import the primary module implicitly. Do
+not include any headers in the module implementation units because that avoids
+duplicated declarations between translation units. This is why non-exported
+using declarations are added from third-party libraries in the primary module
+interface unit.
 
-And if you provide your library as ``libyour_library.so``, you probably need to
-provide a modular one ``libyour_library_modules.so`` since you changed the ABI.
+If the library is provided as ``libyour_library.so``, a modular library (e.g.,
+``libyour_library_modules.so``) may also need to be provided for ABI
+compatibility.
 
 What if there are headers only inclued by the source files
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-The above practice may be problematic if there are headers only included by the source
-files. If you're using private module fragment, you may solve the issue by including them
-in the private module fragment. While it is OK to solve it by including the implementation
-headers in the module purview if you're using implementation module units, it may be
-suboptimal since the primary module interface units now containing entities not belongs
-to the interface.
-
-If you're a perfectionist, maybe you can improve it by introducing internal module partition unit.
+The above practice may be problematic if there are headers only included by the
+source files. If using a private module fragment, this issue may be solved by
----------------
Endilll wrote:

```suggestion
source files. When using a private module fragment, this issue may be solved by
```

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