build: update docker example to bookworm

docker/README.md

@@ -0,0 +1,22 @@
+# Docker sample
+
+## Build image
+
+```shell
+docker build -t actix-docker .
+```
+
+## Run built image
+
+```shell
+docker run -d -p 8080:8080 actix-docker
+# and the server should start instantly
+curl http://localhost:8080
+```
+
+## Running unit tests
+
+```shell
+docker build -t actix-docker:test .
+docker run --rm actix-docker:test
+```