ci: allow attestations in docker workflow

[skip ci]

Change-Id: Id2267f89aebd1517fac0f6566710f52de304b8f7
diff --git a/.github/workflows/docker.yml b/.github/workflows/docker.yml
index a117fbe..492865a 100644
--- a/.github/workflows/docker.yml
+++ b/.github/workflows/docker.yml
@@ -9,8 +9,9 @@
   workflow_dispatch:
 
 permissions:
-  packages: write
+  attestations: write
   id-token: write
+  packages: write
 
 jobs:
   ndncert-build:
diff --git a/README.md b/README.md
index 8e5a5ed..cb2dc27 100644
--- a/README.md
+++ b/README.md
@@ -2,6 +2,7 @@
 
 ![Language](https://img.shields.io/badge/C%2B%2B-17-blue)
 [![CI](https://github.com/named-data/ndncert/actions/workflows/ci.yml/badge.svg)](https://github.com/named-data/ndncert/actions/workflows/ci.yml)
+[![Docker](https://github.com/named-data/ndncert/actions/workflows/docker.yml/badge.svg)](https://github.com/named-data/ndncert/actions/workflows/docker.yml)
 
 The NDN certificate management protocol (**NDNCERT**) enables automatic certificate management
 in NDN. In Named Data Networking (NDN), every entity should have a corresponding identity