docs: add deprecation message for using watson-tokens

Author: dpopp07

README.md

@@ -239,6 +239,8 @@ The Authorization service can generate auth tokens for situations where providin
 
 Tokens are valid for 1 hour and may be sent using the `X-Watson-Authorization-Token` header or the `watson-token` query param.
 
+> _NOTE_: Authenticating with the `X-Watson-Authorization-Token` header is now deprecated. The token continues to work with Cloud Foundry services, but is not supported for services that use Identity and Access Management (IAM) authentication. For details see [Authenticating with IAM tokens](https://console.bluemix.net/docs/services/watson/getting-started-iam.html#iam) or the README in the IBM Watson SDK you use.
+
 Note that the token is supplied URL-encoded, and will not be accepted if it is double-encoded in a querystring.
 
 ```javascript

lib/recognize-stream.ts

@@ -181,6 +181,12 @@ class RecognizeStream extends Duplex {
     const options = this.options;
 
     if (options.token && !options['watson-token']) {
+      console.warn(
+        'Authenticating with the X-Watson-Authorization-Token header is deprecated.' +
+        ' The token continues to work with Cloud Foundry services, but is not' +
+        ' supported for services that use Identity and Access Management (IAM) authentication.' +
+        ' For details see Authenticating with IAM tokens or the README in the IBM Watson SDK you use.'
+      );
       options['watson-token'] = options.token;
     }
     if (options.content_type && !options['content-type']) {