feat: add initial documentation website

- Add MkDocs-based documentation website with Material theme
- Include basic pages: Home, Configuration, Examples, Contributing, Releases
- Add API documentation structure for Table, Catalog, Schema, Types, and Table Scan
- Add build script for local documentation generation
- Add GitHub Actions workflow for automatic deployment to GitHub Pages
- Configure custom domain cpp.iceberg.apache.org

Note: This is a demo version with placeholder content that needs further refinement.

Author: nullccxsy

docs/CNAME

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+cpp.iceberg.apache.org

docs/README.md

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+#!/bin/bash
+
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+PROJECT_ROOT="$(dirname "$SCRIPT_DIR")"
+
+cd "$PROJECT_ROOT"
+
+echo "Building Iceberg C++ documentation..."
+echo "Working directory: $(pwd)"
+
+if ! command -v mkdocs &> /dev/null; then
+    echo "Error: mkdocs is not installed"
+    exit 1
+fi
+
+echo "Installing MkDocs dependencies..."
+pip install mkdocs-material
+
+echo "Building MkDocs documentation..."
+mkdocs build --config-file docs/mkdocs.yml
+
+echo "Documentation build completed successfully!"
+echo "MkDocs site: docs/site/"