docs: use direct link to github for contributing guide

Signed-off-by: Gustavo Inacio <[email protected]>

Author: gusinacio

README.md

@@ -67,4 +67,4 @@ system being off-chain.
 
 Contributions are welcome! Please submit a pull request or open an issue to 
 discuss potential changes.
-Also, make sure to follow the [Contributing Guide](CONTRIBUTING.md).
+Also, make sure to follow the [Contributing Guide](https://github.com/semiotic-ai/timeline-aggregation-protocol/blob/main/CONTRIBUTING.md).