Add information about the monorepo to README and the pull request template.

README.md

@@ -0,0 +1,5 @@
+# This repository has been archived in favor of tensorflow/tfjs.
+
+This repo will remain around for some time to keep history but all future PRs should be sent to [tensorflow/tfjs](https://github.com/tensorflow/tfjs) inside the tfjs-core folder.
+
+All history and contributions have been preserved in the monorepo.

pull_request_template.md

@@ -1,3 +1 @@
-To see the logs from the Cloud Build CI, please join either
-our [discussion](https://groups.google.com/a/tensorflow.org/forum/#!forum/tfjs)
-or [announcement](https://groups.google.com/a/tensorflow.org/forum/#!forum/tfjs-announce) mailing list.
+## This repository has been archived in favor of the monorepo at https://github.com/tensorflow/tfjs. Please send pull requests there.