install: Add wpa-supplicant to the image.

Reported by Amirouche Boubekki <amirouche.boubekki@gmail.com>.

* gnu/system/install.scm (installation-os)[packages]: Add
  WPA-SUPPLICANT.

gnu/system/install.scm

@@ -21,6 +21,7 @@
   #:use-module (guix gexp)
   #:use-module (guix monads)
   #:use-module ((guix store) #:select (%store-prefix))
+  #:use-module (gnu packages admin)
   #:use-module (gnu packages linux)
   #:use-module (gnu packages cryptsetup)
   #:use-module (gnu packages package-management)
@@ -256,7 +257,7 @@ Use Alt-F2 for documentation.
                      parted ddrescue
                      grub                  ;mostly so xrefs to its manual work
                      cryptsetup
-                     wireless-tools
+                     wireless-tools wpa-supplicant
                      ;; XXX: We used to have GNU fdisk here, but as of version
                      ;; 2.0.0a, that pulls Guile 1.8, which takes unreasonable
                      ;; space; furthermore util-linux's fdisk is already