Update README.md: add deprecation warning (#1077)

Co-authored-by: Mike Taylor <[email protected]>

Author: samdutton

README.md

@@ -1,3 +1,13 @@
+**This technology is scheduled for deprecation.**
+
+This repository will be archived and will no longer accept new submissions.
+
+See our [Update on Plans for Privacy Sandbox Technologies](https://privacysandbox.com/news/update-on-plans-for-privacy-sandbox-technologies/).
+
+[Privacy Sandbox feature status](https://privacysandbox.google.com/overview/status) provides more information about the status of individual APIs and platform features.
+
+---
+
 # **Related Website Sets**
 For full instructions and guidance on how to submit a set, please read the [Related Website Sets Submission Guidelines](https://github.com/GoogleChrome/first-party-sets/blob/main/RWS-Submission_Guidelines.md).
 
@@ -21,4 +31,4 @@ The following is a description of the contents of this repository:
     they will fail
 * Reference files like 
 [effective_tld_names.dat](https://github.com/GoogleChrome/first-party-sets/blob/main/effective_tld_names.dat) 
-and [ICANN_domains](https://github.com/GoogleChrome/first-party-sets/blob/main/ICANN_domains)
+and [ICANN_domains](https://github.com/GoogleChrome/first-party-sets/blob/main/ICANN_domains)