Update readme with archive message (#3408)

Co-authored-by: Adam <103067949+AdamL-Microsoft@users.noreply.github.com>

README.md

@@ -1,5 +1,20 @@
 # <img src="docs/onefuzz_text.svg" height="120" alt="OneFuzz" />
 
+# IMPORTANT NOTICE
+
+**_Since September 2020 when OneFuzz was first open sourced, we’ve been on a journey to create a best-in-class orchestrator for running fuzzers, driving security and quality into our products._**
+
+
+**_Initially launched by a small group in MSR, OneFuzz has now become a significant internal platform within Microsoft. As such, we are regretfully archiving the project to focus our attention on becoming a more deeply integrated service within the company. Unfortunately, we aren’t a large enough team to live in both the open-source world and the internal Microsoft world with its own unique set of requirements._**
+
+**_Our current plan is to archive the project in the next few months. That means we’ll still be making updates for a little while. Of course, even after it’s archived, you’ll still be able to fork it and make the changes you need. Once we’ve decided on a specific date for archiving, we’ll update this readme._**
+
+**_Thanks for taking the journey with us._**
+
+**_The OneFuzz team._**
+
+---
+
 [![Onefuzz build status](https://github.com/microsoft/onefuzz/workflows/Build/badge.svg?branch=main)](https://github.com/microsoft/onefuzz/actions/workflows/ci.yml?query=branch%3Amain)
 
 ## A self-hosted Fuzzing-As-A-Service platform