docs: add GitHub Pages documentation deployment workflow

- Create GitHub Actions workflow for deploying documentation to GitHub Pages
- Update README.md with documentation badge and link
- Add missing gem dependency in docs/Gemfile
- Configure Jekyll build and deployment process

.github/workflows/deploy-docs.yml

@@ -0,0 +1,64 @@
+name: Deploy Documentation to GitHub Pages
+
+on:
+  push:
+    branches:
+      - main
+    paths:
+      - 'docs/**'
+      - '.github/workflows/deploy-docs.yml'
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+# Allow only one concurrent deployment
+concurrency:
+  group: "pages"
+  cancel-in-progress: true
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: '3.2'
+          bundler-cache: true
+          cache-version: 0
+
+      - name: Setup Pages
+        uses: actions/configure-pages@v4
+
+      - name: Install dependencies
+        run: |
+          cd docs
+          bundle install
+
+      - name: Build site
+        run: |
+          cd docs
+          bundle exec jekyll build
+        env:
+          JEKYLL_ENV: production
+
+      - name: Upload artifact
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: docs/_site
+
+  deploy:
+    needs: build
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    runs-on: ubuntu-latest
+    steps:
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v4