Add missing documentation.

Author: samuel-williams-shopify

lib/async/grpc/remote_error.rb

@@ -5,7 +5,14 @@
 
 module Async
 	module GRPC
+		# Represents an error that originated from a remote gRPC server.
+		# Used as the `cause` of {Protocol::GRPC::Error} when the client receives a non-OK status.
+		# The message and optional backtrace are extracted from response metadata.
 		class RemoteError < StandardError
+			# Create a RemoteError from server response metadata.
+			# @parameter message [String | Nil] The error message from `grpc-message` header.
+			# @parameter metadata [Hash] Response metadata (extracted from gRPC headers). If it contains a `"backtrace"` key (array of strings), it is set on the error and removed from the hash.
+			# @returns [RemoteError] The constructed error instance.
 			def self.for(message, metadata)
 				self.new(message).tap do |error|
 					if backtrace = metadata.delete("backtrace")