title: Autogenerate REST endpoints from .proto
body: <p>I am having problem with compiling the .proto file. Looking to generate REST endpoints from the .proto files. Below is the code and error : 
  syntax = "proto3";</p>
  
  <pre><code>package pb;
  
  import "google/protobuf/empty.proto";
  import "google/api/annotations.proto";
  
  service UrlShortener {
    rpc Hello(HelloRequest) returns (HelloResponse);
  
    rpc Encrypt(EncryptRequest) returns (EncryptResponse);
  
    rpc Decrypt(DecryptRequest) returns (DecryptResponse) {
      option (google.api.http) = {
                  get: "/{hash}"
              };
    }
  }
  
  message HelloRequest {
    string Name = 1;
  }
  
  message HelloResponse {
    string Message = 1;
  }
  
  message EncryptRequest {
    string OriginalUrl = 1;
  }
  
  message EncryptResponse {
    UrlMap ResponseMap = 1;
  }
  
  message DecryptRequest {
    string hash = 1;
  }
  </code></pre>
  
  <p>Error : 
  github.com/grpc-ecosystem/grpc-gateway/third_party/googleapis: warning: directory does not exist.
  google/api/annotations.proto: File not found.
  urlshortener.proto: Import "google/api/annotations.proto" was not found or had errors.</p>
  
  <p>Please help with fixing this.</p>
  
  <p>I tried : go get -u github.com/grpc-ecosystem/grpc-gateway
  But it failed saying : no buildable go source files in path.</p>