doc: Document disabling cargo phases in Rust builds

Since 042adf0 ("cargo/hooks: allow hooks to be disabled"), it is possible
to disable the default cargo hooks. This allows to switch back to the default
phases from stdenv. This can be useful to package projects that rely on
Makefiles.

doc/languages-frameworks/rust.section.md

@@ -397,9 +397,13 @@ In this scenario, the `checkPhase` will be ran in `debug` mode as well.
 
 Some packages may use custom scripts for building/installing, e.g. with a `Makefile`.
 In these cases, it's recommended to override the `buildPhase`/`installPhase`/`checkPhase`.
-
 Otherwise, some steps may fail because of the modified directory structure of `target/`.
 
+If you want to run targets from a `Makefile`, instead of overriding the phases,
+you can set `dontCargoBuild`/`dontCargoInstall`/`dontCargoCheck` to `true` to
+use the [default phases from `stdenv`](#sec-stdenv-phases), which execute make
+targets and can be controlled by various variables in the derivation.
+
 ### Building a crate with an absent or out-of-date Cargo.lock file {#building-a-crate-with-an-absent-or-out-of-date-cargo.lock-file}
 
 `buildRustPackage` needs a `Cargo.lock` file to get all dependencies in the