network: install wifi-adhoc.network by default, make wifi-{ap,station} examples

I think 80-wifi-adhoc.network is safe enough, since it just enables
the link-local addressing. But the other two enable DHCP in client
or server modes, and we should not do this by default.

network/meson.build

@@ -4,6 +4,9 @@ if conf.get('ENABLE_NETWORKD') == 1
         install_data('80-container-host0.network',
                      '80-container-ve.network',
                      '80-container-vz.network',
+                     '80-wifi-adhoc.network',
+                     '80-wifi-ap.network.example',
+                     '80-wifi-station.network.example',
                      install_dir : networkdir)
 
         meson.add_install_script('sh', '-c',