Update instructions to run protoc on Windows and Linux

generators/tests/org/jetbrains/kotlin/generators/protobuf/GenerateProtoBuf.kt

@@ -15,11 +15,17 @@ import kotlin.system.exitProcess
 // This file generates protobuf classes from formal description.
 // To run it, you'll need protoc (protobuf compiler) 2.6.1 installed.
 //
-// * Windows: download and unpack from here: https://code.google.com/p/protobuf/downloads/list
-// * Ubuntu: install "protobuf-compiler" package
+// * Windows:
+//     Download and unpack binaries from here: https://github.com/protocolbuffers/protobuf/releases/tag/v2.6.1
+// * Linux:
+//     Download and unpack sources from here: https://github.com/protocolbuffers/protobuf/releases/tag/v2.6.1
+//     See README for instructions how to compile the project. Basically something like this should work:
+//       ./autogen.sh
+//       ./configure
+//       make
+//       make install
 // * macOS:
 //     brew install https://raw.githubusercontent.com/udalov/protobuf261/master/protobuf261.rb
-// * You can also download source and build it yourself (https://code.google.com/p/protobuf/downloads/list)
 //
 // You may need to provide custom path to protoc executable, just modify this constant:
 private const val PROTOC_EXE = "protoc"