Update App Engine Java SDK release process documentation and add a pointer for moved internal workflows.

PiperOrigin-RevId: 820704345
Change-Id: I162ab0662c097904f973bad5dca642a098fb3deb

Author: ludoch

google3/third_party/java_src/appengine_standard/INTERNAL_WORKFLOWS_README.md

@@ -0,0 +1,19 @@
+<!--
+ Copyright 2021 Google LLC
+
+ Licensed under the Apache License, Version 2.0 (the "License");
+ you may not use this file except in compliance with the License.
+ You may obtain a copy of the License at
+
+     https://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+-->
+# Internal Workflows for appengine-java-standard
+
+Documentation for internal workflows is there:
+[App Engine Java SDK release process](https://g3doc.corp.google.com/apphosting/g3doc/runtimes/architecture/runtimes/java/appengine_skd_release_process.md#github-mirroring-and-cicd).