fix: confusing wording for billing cycle

docs: update screenshots on readme

includes/i18n/zh_cn.php

@@ -45,6 +45,10 @@ $i18n = [
     "Weekly"          => "每周",
     "Monthly"         => "每月",
     "Yearly"          => "每年",
+    "daily"           => "日",
+    "weekly"          => "周",
+    "monthly"         => "月",
+    "yearly"          => "年",
     "days"            => "天",
     "weeks"           => "周",
     "months"          => "月",
@@ -62,7 +66,7 @@ $i18n = [
     "search_logo"     => "在网上搜索 Logo",
     "web_search"      => "网页搜索",
     "currency"        => "货币",
-    "billing_cycle"   => "账单周期",
+    "payment_every"   => "支付频率",
     "frequency"       => "频率",
     "cycle"           => "周期",
     "next_payment"    => "下次支付",