extend cmake docs

docs/source/usage/project_integration.md

@@ -57,25 +57,59 @@ If you are using pystencils-sfg with CMake through the provided CMake module,
 
 ### Add the module
 
-To include the module in your CMake source tree, a separate find module is provided.
-You can use the global CLI to obtain the find module; simply run
+To include the module in your CMake source tree, you must first add the pystencils-sfg *Find-module*
+to your CMake module path.
+To create the Find-module, navigate to the directory it should be placed in and run the following command:
 
 ```shell
 sfg-cli cmake make-find-module
 ```
 
-to create the file `FindPystencilsSfg.cmake` in the current directory.
-Add it to the CMake module path, and load the *pystencils-sfg* module via *find_package*:
+This will create the `FindPystencilsSfg.cmake` file.
+Make sure that its containing directory is added to the CMake module path.
+
+To load pystencils-sfg into CMake, we first need to set the Python interpreter
+of the environment SFG is installed in.
+There are several ways of doing this:
+
+#### Set Python via a Find-Module Hint
+
+Set the `PystencilsSfg_PYTHON_PATH` hint variable inside your `CMakeLists.txt` to point at the
+Python executable which should be used to invoke pystencils-sfg, e.g.:
 
 ```CMake
-find_package( PystencilsSfg )
+set(PystencilsSfg_PYTHON_PATH ${CMAKE_SOURCE_DIR}/.venv/bin/python)
+```
+
+This is the recommended way, especially when other parts of your project also use Python.
+
+#### Set Python via a Cache Variable
+
+On the command line or in a [CMake configure preset](https://cmake.org/cmake/help/latest/manual/cmake-presets.7.html),
+set the `PystencilsSfg_PYTHON_INTERPRETER` cache variable to point at the Python executable to be used to invoke pystencils-sfg;
+e.g.:
+
+```bash
+cmake -S . -B build -DPystencilsSfg_PYTHON_INTERPRETER=`pwd`/.venv/bin/python
 ```
 
-Make sure to set the `Python_ROOT_DIR` cache variable to point to the correct Python interpreter
-(i.e. the virtual environment you have installed *pystencils-sfg* into).
+If both the cache variable and the `PystencilsSfg_PYTHON_PATH` hint are set, the cache variable takes precedence,
+so you can use the cache variable to override the hint.
+
+#### Automatically Find a Python Installation
+
+If none of the above is provided, pystencils-sfg will invoke [FindPython](https://cmake.org/cmake/help/latest/module/FindPython.html)
+to determine the Python interpreter it should use.
+You can affect this process through any of the hints listed in the `FindPython` documentation.
+
+#### Find pystencils-sfg
+
+Finally, call `find_package( PystencilsSfg )` from your `CMakeLists.txt` to load the SFG module.
+If SFG as a dependency is not optional, add the `REQUIRED` flag such that the call will fail if
+the package cannot be found.
 
 (cmake_add_generator_scripts)=
-### Add generator scripts
+### Adding Generator Scripts
 
 The primary interaction point in CMake is the function `pystencilssfg_generate_target_sources`,
 with the following signature:
@@ -105,15 +139,21 @@ The function takes the following options:
    If set, this overrides the value of `PystencilsSfg_CONFIG_MODULE`
    in the current scope (see [](#cmake_set_config_module))
 
-### Include generated files
+Any C++ header files generated by the above call can be included in any files belonging to `target` via:
 
-The `pystencils-sfg` CMake module creates a subfolder `sfg_sources/gen` at the root of the build tree
-and writes all generated source files into it. The directory `sfg_sources` is added to the project's include
-path, such that generated header files for a target `<target>` may be included via:
 ```C++
-#include "gen/<target>/kernels.h"
+#include "gen/<file1.hpp>"
+#include "gen/<file2.hpp>"
+/* ... */
 ```
 
+### Changing the Output Directory
+
+The CMake function listed above will create a subdirectory `_gen/<target>` at the current point in
+the build tree (i.e. [`CMAKE_CURRENT_BINARY_DIR`](https://cmake.org/cmake/help/latest/variable/CMAKE_CURRENT_BINARY_DIR.html)).
+This directory is placed on the include path of `<target>`, and the generated files will be written to `_gen/<target>/gen/`
+such that they can be included with the `gen` prefix.
+
 (cmake_set_config_module)=
 ### Set a Configuration Module