Minor, update instructions for installing protobuf261 + regenerate

generators/protobuf/GenerateProtoBuf.kt

@@ -22,7 +22,8 @@ import kotlin.system.exitProcess
 //       make
 //       make install
 // * macOS:
-//     brew install https://raw.githubusercontent.com/udalov/protobuf261/master/protobuf261.rb
+//     curl -L https://raw.githubusercontent.com/udalov/protobuf261/master/protobuf261.rb > protobuf261.rb
+//     brew install protobuf261.rb
 //
 // You may need to provide custom path to protoc executable, just modify this constant:
 private const val PROTOC_EXE = "protoc"

plugins/kotlinx-serialization/kotlinx-serialization.k1/src/org/jetbrains/kotlinx/serialization/compiler/extensions/SerializationPluginMetadataExtensions.java

@@ -1,5 +1,5 @@
 // Generated by the protocol buffer compiler.  DO NOT EDIT!
-// source: plugins/kotlin-serialization/kotlin-serialization-compiler/src/class_extensions.proto
+// source: plugins/kotlinx-serialization/kotlinx-serialization.k1/src/class_extensions.proto
 
 package org.jetbrains.kotlinx.serialization.compiler.extensions;