doc/stdenv: Clarify that the wrappers come with hooks

doc/stdenv/stdenv.chapter.md

@@ -1120,7 +1120,7 @@ This sets `SOURCE_DATE_EPOCH` to the modification time of the most recent file.
 Many other packages provide hooks, that are not part of `stdenv`. You can find
 these in the [Hooks Reference](#chap-hooks).
 
-### Bintools Wrapper {#bintools-wrapper}
+### Bintools Wrapper and hook {#bintools-wrapper}
 
 The Bintools Wrapper wraps the binary utilities for a bunch of miscellaneous purposes. These are GNU Binutils when targeting Linux, and a mix of cctools and GNU binutils for Darwin. \[The “Bintools” name is supposed to be a compromise between “Binutils” and “cctools” not denoting any specific implementation.\] Specifically, the underlying bintools package, and a C standard library (glibc or Darwin’s libSystem, just for the dynamic loader) are all fed in, and dependency finding, hardening (see below), and purity checks for each are handled by the Bintools Wrapper. Packages typically depend on CC Wrapper, which in turn (at run time) depends on the Bintools Wrapper.
 
@@ -1130,7 +1130,7 @@ A final task of the setup hook is defining a number of standard environment vari
 
 A problem with this final task is that the Bintools Wrapper is honest and defines `LD` as `ld`. Most packages, however, firstly use the C compiler for linking, secondly use `LD` anyways, defining it as the C compiler, and thirdly, only so define `LD` when it is undefined as a fallback. This triple-threat means Bintools Wrapper will break those packages, as LD is already defined as the actual linker which the package won’t override yet doesn’t want to use. The workaround is to define, just for the problematic package, `LD` as the C compiler. A good way to do this would be `preConfigure = "LD=$CC"`.
 
-### CC Wrapper {#cc-wrapper}
+### CC Wrapper and hook {#cc-wrapper}
 
 The CC Wrapper wraps a C toolchain for a bunch of miscellaneous purposes. Specifically, a C compiler (GCC or Clang), wrapped binary tools, and a C standard library (glibc or Darwin’s libSystem, just for the dynamic loader) are all fed in, and dependency finding, hardening (see below), and purity checks for each are handled by the CC Wrapper. Packages typically depend on the CC Wrapper, which in turn (at run-time) depends on the Bintools Wrapper.