doc: document buildPython* stdenv overriding via <function>.override

doc/languages-frameworks/python.section.md

@@ -542,6 +542,10 @@ are used in [`buildPythonPackage`](#buildpythonpackage-function).
   with the `pipInstallHook`.
 - `unittestCheckHook` will run tests with `python -m unittest discover`. See [example usage](#using-unittestcheckhook).
 
+#### Overriding build helpers {#overriding-python-build-helpers}
+
+Like most of the build helpers provided by Nixpkgs, most Python build helpers provide a `<function>.override` attributes. It works like [<pkg>.override](#sec-pkg-override), and can be used to override the dependencies of each build helper. Specifically, the `stdenv` used by `buildPythonPackage` and `buildPythonApplication`, which defaults to `python.stdenv`, can be overridden with `buildPythonPackage.override { stdenv = customStdenv; }` and `buildPythonApplication.override { stdenv = customStdenv; }`, respectively.
+
 ## User Guide {#user-guide}
 
 ### Using Python {#using-python}

doc/redirects.json

@@ -3406,6 +3406,9 @@
   "buildpythonpackage-parameters": [
     "index.html#buildpythonpackage-parameters"
   ],
+  "overriding-python-build-helpers": [
+    "index.html#overriding-python-build-helpers"
+  ],
   "overriding-python-packages": [
     "index.html#overriding-python-packages"
   ],