[PATCH] Post-merge README with a disclaimer

[Roman Arutyunyan]

# HG changeset patch
# User Roman Arutyunyan <arut at nginx.com>
# Date 1684568499 -14400
#      Sat May 20 11:41:39 2023 +0400
# Branch quic
# Node ID a83071314a22652d4a552e72e13d18aa4c01d79e
# Parent  e92a03d1d6dad22866e9e5e09fac8545cbdb15e4
Post-merge README with a disclaimer.

diff --git a/README b/README
new file mode 100644
--- /dev/null
+++ b/README
@@ -0,0 +1,5 @@
+This code was merged[1] into mainline nginx[2].
+This repository is considered read-only now.  Don’t use it for anything.
+
+[1] https://hg.nginx.org/nginx/rev/235d482ef6bc
+[2] https://hg.nginx.org/nginx