remove all instances of nix-env -i without -A in the NixOS manual

motivation: https://nixos.wiki/wiki/FAQ/Why_not_use_nix-env_-i_foo%3F

nixos/doc/manual/installation/installing.xml

@@ -335,7 +335,7 @@
      If you’re using the graphical ISO image, other editors may be available
      (such as <command>vim</command>). If you have network access, you can also
      install other editors — for instance, you can install Emacs by running
-     <literal>nix-env -i emacs</literal>.
+     <literal>nix-env -f '&lt;nixpkgs&gt;' -iA emacs</literal>.
     </para>
     <variablelist>
      <varlistentry>
@@ -467,10 +467,10 @@ Retype new UNIX password: ***</screen>
     <para>
      You may also want to install some software. For instance,
 <screen>
-<prompt>$ </prompt>nix-env -qa \*</screen>
+<prompt>$ </prompt>nix-env -qaP \*</screen>
      shows what packages are available, and
 <screen>
-<prompt>$ </prompt>nix-env -i w3m</screen>
+<prompt>$ </prompt>nix-env -f '&lt;nixpkgs&gt;' -iA w3m</screen>
      install the <literal>w3m</literal> browser.
     </para>
    </listitem>

nixos/modules/services/editors/emacs.xml

@@ -552,7 +552,7 @@ emacsclient --create-frame --tty  # opens a new frame on the current terminal
     <xref linkend="opt-environment.systemPackages"/>
     (<link
       linkend="sec-declarative-package-mgmt">NixOS</link>), or run
-    <literal>nix-env -i pkgs.docbook5</literal>
+    <literal>nix-env -f '&lt;nixpkgs&gt;' -iA docbook5</literal>
     (<link linkend="sec-ad-hoc-packages">Nix</link>).
    </para>