chore: Included the digest for the docker image

- https://cloud.google.com/architecture/using-container-images
- https://github.com/ossf/scorecard/blob/main/docs/checks.md#pinned-dependencies

Dockerfile

@@ -1,4 +1,7 @@
-FROM python:3
+# using container digest is recommended https://github.com/opencontainers/image-spec/blob/main/descriptor.md#digests 
+# https://cloud.google.com/architecture/using-container-images
+
+FROM python:3@sha256:b7bfea0126f539ba570a01fb595ee84cc4e7dcac971ad83d12c848942fa52cb6
 
 WORKDIR /usr/src
 COPY requirements.txt ./
@@ -8,4 +11,4 @@ WORKDIR /usr/src/hosts
 
 # Now you launch this with
 #  $ docker build ./
-#  $ docker run -it (containerid) bash
+#  $ docker run -it (containerid) bash