Document new-install's completion

[ci skip]

Cabal/ChangeLog.md

 # 2.4.0.0 (current development version)
+  * Add `readGhcEnvironmentFile` to parse GHC environment files.
   * Drop support for GHC 7.4, since it is out of our support window
     (and has been for over a year!)
   * Deprecate `preSDist`, `sDistHook`, and `postSDist` in service of 

Cabal/doc/nix-local-build.rst

@@ -461,8 +461,9 @@ invocations and bringing the project's executables into scope.
 cabal new-install
 -----------------
 
-``cabal new-install [FLAGS] PACKAGES`` builds the specified nonlocal packages
-and symlinks their executables in ``symlink-bindir`` (usually ``~/.cabal/bin``).
+``cabal new-install [FLAGS] PACKAGES`` builds the specified packages, adds their
+libraries into the default environment and symlinks their executables in
+``symlink-bindir`` (usually ``~/.cabal/bin``).
 
 For example this command will build the latest ``cabal-install`` and symlink
 its ``cabal`` executable:
@@ -515,16 +516,6 @@ byte) that must be satisfied for it to function correctly in the larger new-buil
 ``autogen-modules`` is able to replace uses of the hooks to add generated modules, along with
 the custom publishing of Haddock documentation to Hackage.
 
-Unsupported commands
---------------------
-
-The following commands are not currently supported:
-
-``cabal new-install`` (libraries and local executables)
-    (:issue:`3737` and :issue:`4558`)
-    Workaround: no good workaround at the moment. (But note that you no
-    longer need to install libraries before building!)
-
 Configuring builds with cabal.project
 =====================================
 

cabal-install/changelog

 -*-change-log-*-
 
 2.4.0.0 (current development version)
+	* 'new-install' now supports installing libraries and local 
+	  components. (#5399)
 	* Drop support for GHC 7.4, since it is out of our support window
       (and has been for over a year!)
 	* 'new-update' now works outside of projects. (#5096)