title: How to GPG sign a file that is built by Travis-CI
body: <p>I see that Travis has a workflow for encrypting a files, <a href="https://docs.travis-ci.com/user/encrypting-files/" rel="noreferrer">here</a>.</p>
  
  <p>My use case is slightly simpler, I just want to generate a signature for a file that has been built on Travis-CI.
  Say:</p>
  
  <pre><code>hello-0.0.1-a.bin.asc
  hello-0.0.1-a.bin
  pubkey.gpg 
  &lt;or&gt; hello-0.0.1-a.pub
  </code></pre>
  
  <p>In this case <code>hello-0.0.1-a.bin</code> is created by a Travis build, and will be pushed to Github as a release.
  Likewise the signature must also be pushed to Github as a release (i.e. under the same tag).  </p>
  
  <p>I don't strongly care (i.e. not a deal breaker) if the private/public key-pair is unique to that build.
  But it would be ideal if the private/public key-pair is shared between builds.</p>
  
  <p>Appreciate and hints tips or incantations.</p>