firejail: clarify wrappedBinaries option description

I had trouble getting programs.firejail.wrappedBinaries to have any effect on my
system (#152852), because I did not realise that "put[ting] the actual
application binary in the global environment" included adding the program
package to environment.systemPackages, and I thought that the package must be
present for this option to take effect.  I have added a clarifying parenthetical
statement explicitly mentioning environment.systemPackages in this caveat.

1 files changed, 4 insertions, 2 deletions

diff --git a/nixos/modules/programs/firejail.nix b/nixos/modules/programs/firejail.nix
index 41db4f0136e..8c10d7c4df3 100644
--- a/nixos/modules/programs/firejail.nix
+++ b/nixos/modules/programs/firejail.nix
@@ -74,8 +74,10 @@ in {
         </para>
         <para>
         You will get file collisions if you put the actual application binary in
-        the global environment and applications started via .desktop files are
-        not wrapped if they specify the absolute path to the binary.
+        the global environment (such as by adding the application package to
+        <code>environment.systemPackages</code>), and applications started via
+        .desktop files are not wrapped if they specify the absolute path to the
+        binary.
       '';
     };
   };