po: Update POTFILES.in.

* po/guix/POTFILES.in: Add missing files that contain messages to be
translated.

po/guix/POTFILES.in

@@ -5,10 +5,23 @@ gnu/packages.scm
 gnu/services.scm
 gnu/system.scm
 gnu/services/shepherd.scm
+gnu/system/file-systems.scm
+gnu/system/image.scm
+gnu/system/linux-container.scm
 gnu/system/mapped-devices.scm
 gnu/system/shadow.scm
 guix/import/egg.scm
+guix/import/cpan.scm
+guix/import/cran.scm
+guix/import/elpa.scm
+guix/import/github.scm
+guix/import/git.scm
+guix/import/gnu.scm
+guix/import/go.scm
+guix/import/minetest.scm
 guix/import/opam.scm
+guix/import/pypi.scm
+guix/import/texlive.scm
 gnu/installer.scm
 gnu/installer/connman.scm
 gnu/installer/hostname.scm
@@ -47,6 +60,10 @@ guix/scripts.scm
 guix/scripts/build.scm
 guix/diagnostics.scm
 guix/discovery.scm
+guix/ci.scm
+guix/cve.scm
+guix/git-authenticate.scm
+guix/gnupg.scm
 guix/lint.scm
 guix/scripts/download.scm
 guix/scripts/package.scm
@@ -92,13 +109,20 @@ guix/http-client.scm
 guix/nar.scm
 guix/narinfo.scm
 guix/channels.scm
+guix/packages.scm
 guix/profiles.scm
+guix/remote.scm
+guix/ssh.scm
 guix/git.scm
+guix/substitutes.scm
 guix/deprecation.scm
 guix/derivations.scm
 guix/scripts/archive.scm
 guix/scripts/build.scm
+guix/scripts/discover.scm
 guix/scripts/environment.scm
+guix/scripts/home/import.scm
+guix/scripts/home.scm
 guix/scripts/time-machine.scm
 guix/scripts/import/cpan.scm
 guix/scripts/import/crate.scm