python3Packages.lttng: Explain use of PYTHON environment variable

pkgs/development/python-modules/lttng/default.nix

@@ -20,6 +20,10 @@ toPythonModule (lttng-tools.overrideAttrs ({ nativeBuildInputs ? [ ], configureF
     "--disable-man-pages"
   ];
 
+  # Nix treats nativeBuildInputs specially for cross-compilation, but in this
+  # case, cross-compilation is accounted for explicitly. Using the variables
+  # ensures that the platform setup isn't messed with further. It also allows
+  # regular Python to be added in the future if it is ever needed.
   PYTHON = "${python.pythonOnBuildForHost}/bin/python";
   PYTHON_CONFIG = "${python.pythonOnBuildForHost}/bin/python-config";
 }))