docs(readme): add silent option example to code usage section

Author: Tapppi

README.md

@@ -122,13 +122,17 @@ standard-version --help
 
 ## Code usage
 
+Use the `silent` option to stop `standard-version` from printing anything
+to the console.
+
 ```js
 var standardVersion = require('standard-version')
 
 // Options are the same as command line, except camelCase
 standardVersion({
   noVerify: true,
-  infile: 'docs/CHANGELOG.md'
+  infile: 'docs/CHANGELOG.md',
+  silent: true
 }, function (err) {
   if (err) {
     console.error(`standard-version failed with message: ${err.message}`)