chore(docs): added missing config.transport doc (#5444)

README.md

@@ -492,6 +492,9 @@ These are the available config options for making requests. Only the `url` is re
   // Only either `socketPath` or `proxy` can be specified.
   // If both are specified, `socketPath` is used.
   socketPath: null, // default
+
+  // `transport` determines the transport method that will be used to make the request. If defined, it will be used. Otherwise, if `maxRedirects` is 0, the default `http` or `https` library will be used, depending on the protocol specified in `protocol`. Otherwise, the `httpFollow` or `httpsFollow` library will be used, again depending on the protocol, which can handle redirects.
+  transport: undefined, // default
 
   // `httpAgent` and `httpsAgent` define a custom agent to be used when performing http
   // and https requests, respectively, in node.js. This allows options to be added like