docs(README): require wrapper generation

- Remove pre-generated wrappers claim; generator required per Qt version.
- Document default output (../generated_cpp) and PYTHONQT_GENERATED_PATH.
- Add qmake toggles (generator_only/exclude_generator)

Author: jcfr

README.md

@@ -31,10 +31,9 @@ see https://github.com/danmar/simplecpp. It is licensed under the `0BSDL` licens
 see the `LICENSE` file in the generator/simplecpp directory.
 Copyright (C) 2016-2023 simplecpp team
 
-The generated wrappers are pre-generated and checked-in, so you only
-need to build and run the generator when you want to build additional wrappers
-or you want to upgrade/downgrade to another Qt version, but this requires
-updating the typesystems as well.
+Wrappers are **not** shipped pre-generated. You must run the generator to
+create wrappers for your Qt version (recommended). The repository may keep a
+single example tree (e.g., `generated_cpp_515`) only as a reference.
 
 # Building
 
@@ -93,6 +92,21 @@ First, you need to set a couple of environment variables, which depend on your P
 
    `<generator-executable> qtscript_masterinclude.h build_all.txt`
 
+
+**Output location:** by default the generator emits to `../generated_cpp`
+(relative to the build). You can override this with:
+
+```
+qmake PYTHONQT_GENERATED_PATH=/abs/path/to/generated_cpp
+```
+
+#### qmake toggles (optional)
+
+* `CONFIG+=generator_only`: build only the wrapper generator.
+* `CONFIG+=exclude_generator`: build everything **except** the generator.
+
+Use these to (1) build the generator, (2) run it to produce `generated_cpp`, then (3) build the rest without rebuilding the generator.
+
 ### PythonQt Runtime
 
 Next, we need the PythonQt runtime.