docs: make text more specific about Nix 2.4 support

README.md

@@ -65,7 +65,8 @@ Currently the easiest way to install Home Manager is as follows:
     control this option using the
     [`nix.allowedUsers`][nixosAllowedUsers] system option.
 
-    Note that Nix 2.4 (`nixUnstable`) is not yet supported.
+    Note that Nix 2.4 is not yet fully supported. Most significantly,
+    Home Manager is incompatible with the new `nix profile` command.
 
 2.  Add the appropriate Home Manager channel. If you are following
     Nixpkgs master or an unstable channel you can run

docs/installation.adoc

@@ -36,6 +36,9 @@ root user. For a multi-user install of Nix this means that your user
 must be covered by the {nix-allowed-users}[`allowed-users`] Nix
 option. On NixOS you can control this option using the
 {nixos-allowed-users}[`nix.allowedUsers`] system option.
++
+Note that Nix 2.4 is not yet fully supported. Most significantly, Home
+Manager is incompatible with the new `nix profile`.
 
 2. Add the Home Manager channel that you wish to follow. If you are
 following Nixpkgs master or an unstable channel then this is done by