Merge pull request KnpLabs#722 from nazar-pc/patch-1

Fix example (file contents is needed, not path)

Author: acrobat

doc/security.md

@@ -66,6 +66,7 @@ $jwt = (new Builder)
     ->setIssuer($integrationId)
     ->setIssuedAt(time())
     ->setExpiration(time() + 60)
+    // `file://` prefix for file path or file contents itself
     ->sign(new Sha256(),  new Key('file:///path/to/integration.private-key.pem'))
     ->getToken();
 
@@ -76,4 +77,4 @@ $github->authenticate($token['token'], null, Github\Client::AUTH_HTTP_TOKEN);
 ```
 
 The `$integrationId` you can find in the about section of your github app.
-The `$installationId` you can find by installing the app and using the id in the url.
+The `$installationId` you can find by installing the app and using the id in the url.