docs: deprecation notice

PROXY_GATEWAY_URL block and car backends were migrated
to Rainbow, bifrost-gateway is no longer maintained and runs old boxo
version.

The intention of this change is to make the last release
that will be picked up by people running docker `latest` release,
allowing them to migrate at their own convenience.

Once we have the last release, we can archive the repo, to reduce
confusion.

If someone still needs this, they can fork, but most of existing users
will be happy with Rainbow as drop-in replacement.

README.md

@@ -1,3 +1,22 @@
+> [!WARNING]
+>
+> # ⚠️  `bifrost-gateway` is no longer maintained
+>
+> You can continue using it, but it won't receive any security updates or
+> fixes. Consider forking or migrating to [Rainbow](https://github.com/ipfs/rainbow/).
+>
+> ## ℹ️ Migrating to Rainbow 🌈
+>
+> The `PROXY_GATEWAY_URL` functionality is backported to [Rainbow](https://github.com/ipfs/rainbow/).
+>
+> To use Rainbow with a remote block or CAR backend, configure it with:
+>
+>  `RAINBOW_REMOTE_BACKENDS=<gwurl>`
+>  `RAINBOW_REMOTE_BACKENDS_MODE=block|car`
+>
+> For configuration details, visit:
+> https://github.com/ipfs/rainbow/blob/main/docs/environment-variables.md
+
 bifrost-gateway
 =======================
 

main.go

@@ -71,6 +71,7 @@ See documentation at: https://github.com/ipfs/bifrost-gateway/#readme`,
 		}
 
 		log.Printf("Starting %s %s", name, version)
+
 		registerVersionMetric(version)
 
 		tp, shutdown, err := newTracerProvider(cmd.Context())
@@ -102,6 +103,47 @@ See documentation at: https://github.com/ipfs/bifrost-gateway/#readme`,
 				return err
 			}
 		} else if len(proxyGateway) != 0 {
+			log.Printf(`
+
+⚠️  PROJECT NO LONGER MAINTAINED
+
+  The bifrost-gateway project is no longer maintained.
+
+  You can continue using it, but it won't receive any security updates or
+  fixes. Consider forking or migrating to Rainbow.
+
+ℹ️ MIGRATING TO RAINBOW
+
+  The PROXY_GATEWAY_URL functionality is backported to Rainbow
+  https://github.com/ipfs/rainbow/
+
+  To use Rainbow with a remote block or CAR backend, configure it with:
+  RAINBOW_REMOTE_BACKENDS=<gwurl>
+  RAINBOW_REMOTE_BACKENDS_MODE=block|car
+
+  For details, visit:
+  at https://github.com/ipfs/rainbow/blob/main/docs/environment-variables.md
+
+
+  TLDR:
+
+	If you currently use:
+
+    PROXY_GATEWAY_URL=http://127.0.0.1:8080 \
+    GRAPH_BACKEND=false \
+    ./bifrost-gateway
+
+    It can be replaced with:
+
+    RAINBOW_REMOTE_BACKENDS=http://127.0.0.1:8080 \
+    RAINBOW_REMOTE_BACKENDS_MODE=block \
+    ./rainbow
+
+	Rainbow docker images:
+	https://github.com/ipfs/rainbow#docker
+
+`)
+
 			log.Printf("Proxy backend (PROXY_GATEWAY_URL) at %s", strings.Join(proxyGateway, " "))
 			bs = newProxyBlockStore(proxyGateway, cdns)
 		} else {

version.json

@@ -1,3 +1,3 @@
 {
-  "version": "v0.0.21"
+  "version": "v0.0.22"
 }