docs: add license header to CONTRIBUTING

Author: dheeraj12347

CONTRIBUTING.md

@@ -1,21 +1,38 @@
+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.
+
 # Contributing to iceberg-cpp
 
-This document describes how to set up a development environment, run tests, and use existing tooling such as Docker and pre-commit for iceberg-cpp. [][]
+This document describes how to set up a development environment, run tests, and use existing tooling such as Docker and pre-commit for iceberg-cpp.
 
 ## Development environment
 
-The project can be built and developed using the existing Docker-based environment. Please refer to the README and Doxygen documentation for more detailed API and usage information. [][][]
+The project can be built and developed using the existing Docker-based environment. Please refer to the README and Doxygen documentation for more detailed API and usage information.
 
 ### Local prerequisites
 
 - Git
 - CMake and a C++17-compatible compiler
 - Python (for pre-commit)
-- Docker (recommended for a consistent dev environment) [][]
+- Docker (recommended for a consistent dev environment)
 
 ## Building and testing
 
-Typical steps (refer to README for exact commands and options): [][]
+Typical steps (refer to README for exact commands and options):
 
 ```bash
 mkdir build