Redirect for AS error message regarding SDK license agreements

- error message will provide a link to doc about importing
  license agreements from another workstatio
- Doc currently on TAC, may move to DAC

Change-Id: Iee2839f1dc7b6a5a1fb5a90ad499e1b0cddf5068

docs/html/_redirects.yaml

@@ -841,6 +841,8 @@ redirects:
   to: /studio/run/index.html#instant-run
 - from: /r/studio-ui/test-recorder.html
   to: http://tools.android.com/tech-docs/test-recorder
+- from: /r/studio-ui/export-licenses.html
+  to: http://tools.android.com/tech-docs/new-build-system/license
 - from: /reference/org/apache/http/...
   to: /about/versions/marshmallow/android-6.0-changes.html#behavior-apache-http-client
 - from: /shareables/...