title: Add submodule with specific tag not branch in one command
body: <p>For a rails template I'd like to add a submodule of a specific tag to new rails apps. To keep this simple I'd like to avoid going into subdirectories and running git commands there.</p>
  
  <p><code>git submodule add --branch v1.3.37 git@example.com:foo.git vendor/foo</code></p>
  
  <p>Is what I would like to use, but it does not accept tags for the <code>--branch</code> parameter:</p>
  
  <p><code>fatal: 'origin/v1.3.37' is not a commit and a branch 'v1.3.37 cannot be created from it Unable to checkout submodule 'vendor/foo'</code></p>
  
  <p>Is there a simple way to add a git submodule on a specific tag?</p>