Mark repository as deprecated

Add deprecation note

Author: sqrrrl

README.md

@@ -1,5 +1,12 @@
 # Google Workspace Solutions Gallery
 
+## Note: This repository is deprecated
+
+The solutions contained here have been moved to to [Apps Script Samples repository](https://github.com/googleworkspace/apps-script-samples/tree/main/solutions).
+Refer to the new location for updated versions of these projects.
+
+## Welcome
+
 Welcome to the repository for the [Google Workspace Solutions Gallery](https://developers.google.com/gsuite/solutions/).
 Here you will find end to end use cases to inspire you implement your own for your business needs.
 Try one out today! To get started coding, browse our [developer documentation](https://developers.google.com/gsuite/).