title: how to compile .proto + .options file using nanopb
body: <p>i wrote an .options file and placed it in the same directory as the .proto file.
  then, I tried to compile it (using nanopb compiler) by using the command</p>
  
  <pre><code>generator-bin/protoc --nanopb_out=. message.proto -s message.options
  </code></pre>
  
  <p>and got this error:</p>
  
  <pre><code>Unknown flag: -s
  </code></pre>
  
  <p>so what am I doing wrong? 
  do I need to import my options file in the .proto file?
  is there anything else I should do to make it work?</p>