Add v0.2.1 to docs

.github/workflows/github-pages.yaml

@@ -16,6 +16,7 @@ jobs:
         docs:
           # { ref: <branch/tag name>, name: <docs drop down entry> }
           - { ref: main, name: latest }
+          - { ref: v0.2.1, name: 0.2.1 }
     steps:
       - uses: actions/checkout@v4
         if: ${{ matrix.docs.ref == 'main' }}