Add relay message type enums

lib/nostr/relay_message_type.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+module Nostr
+  # Clients can send 4 types of messages, which must be JSON arrays
+  module RelayMessageType
+    # @return [String] Used to notify clients all stored events have been sent
+    EOSE = 'EOSE'
+
+    # @return [String] Used to send events requested to clients
+    EVENT = 'EVENT'
+
+    # @return [String] Used to send human-readable messages to clients
+    NOTICE = 'NOTICE'
+
+    # @return [String] Used to notify clients if an EVENT was successful
+    OK = 'OK'
+  end
+end