fix: confusing wording for billing cycle

docs: update screenshots on readme

includes/i18n/zh_tw.php

@@ -42,6 +42,10 @@ $i18n = [
     "Weekly"          => "每週",
     "Monthly"         => "每月",
     "Yearly"          => "每年",
+    "daily"           => "日",
+    "weekly"          => "週",
+    "monthly"         => "月",
+    "yearly"          => "年",
     "days"            => "天",
     "weeks"           => "週",
     "months"          => "月",
@@ -58,7 +62,7 @@ $i18n = [
     "search_logo"     => "在網路上搜尋圖示",
     "web_search"      => "網頁搜尋",
     "currency"        => "貨幣",
-    "billing_cycle"   => "帳單週期",
+    "payment_every"   => "付款頻率",
     "frequency"       => "頻率",
     "cycle"           => "週期",
     "next_payment"    => "下次付款",