Add arch repos (#1)

* Add Arch repository domains
Co-authored-by: redtrillix <54786587+redtrillix@users.noreply.github.com>

cache_domains.json

@@ -1,5 +1,10 @@
 {
 	"cache_domains": [
+		{
+			"name": "arch",
+			"description": "Arch Linux based repositories",
+			"domain_files": ["arch.txt"]
+		},
 		{
 			"name": "arenanet",
 			"description": "CDN for guild wars, HoT",