title: Import vendor proto on own proto
body: <p>How to import external (on vendor folder) proto into my own proto?</p>
  
  <p>I'm using this:</p>
  
  <pre><code>syntax = "proto3";
  package command;
  option go_package = "api";
  
  import "github.com/service/command.proto";
  
  service CommandService {
      rpc Push(Command) returns (PushResponse);
  }
  
  message PushResponse {
      string id = 1;
  }
  </code></pre>
  
  <p>But I get an error that the file was not found:</p>
  
  <pre><code>&gt; protoc -I api api/command.proto --go_out=plugins=grpc:api
  github.com/service/command.proto: File not found.
  </code></pre>
  
  <p>Also this gives the same error:</p>
  
  <pre><code>&gt; protoc -I api -I vendor/github.com/service api/command.proto --go_out=plugins=grpc:api
  github.com/service/command.proto: File not found.
  </code></pre>
  
  <p>I tried prefixing with <code>vendor/</code> on .proto file as well with no success.</p>