Add CONTRIBUTING.md

Based on the company template

CONTRIBUTING.md

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+# Contributing
+
+## License
+
+This project is distributed under the Apache-2.0 license. Every source file
+should start with a header comment specifying the license using an [SPDX license
+identifier](https://spdx.dev/learn/handling-license-info/) along with a
+copyright notice. E.g., for an OCaml file:
+
+```ocaml
+(* SPDX-License-Identifier: Apache-2.0
+ * Copyright (c) <date> <author> <email>
+ *)
+```
+
+Note that:
+
+- The holder, on the copyright line, is the name of individual
+  contributors and/or their company;
+- When adding a significant new contribution to a file (i.e. more like
+  whole new features, rather than simple fixes), check whether there
+  already is a copyright for your copyright holder (see above):
+  - If there is one, mentioning any year, it is not required to add
+    the current year (but this is allowed). In no case should you
+    replace the existing year with the current one.
+  - If there is no line for your copyright holder, you should add one,
+    with the current year.
+
+For example, for a source file with multiple contributors spanning
+several years, the copyright lines may look as follows:
+
+```ocaml
+(* SPDX-License-Identifier: Apache-2.0
+ * Copyright (c) 2024-2025 Puneeth Chaganti <[email protected]>
+ * Copyright (c) 2025-2025 Tarides <[email protected]>
+ *)
+```