Update example file

- Add the defaults for the two variables that CI will for the registry and tag when creating container images.
- Add a comment explaining what these are for

Author: korlaxxalrok

.env.example

@@ -11,3 +11,9 @@ CSRF_TRUSTED_ORIGINS='http://127.0.0.1:8000,http://localhost:8000'
 
 SECRET_KEY='secret_key'
 DEBUG='True'
+
+# Add the following to your local .env file. They will be used in the CI process
+# and you can largely forget about them, but including them in your .env file
+# will act like a safe default and help suppress warnings.
+REGISTRY=""
+TAG=""