Add license note

Author: benbrandt

README.md

@@ -54,3 +54,7 @@ Pull requests should intend to close [an existing issue](https://github.com/zed-
 
 - **Bug Reports**: If you notice a bug in the protocol, please file [an issue](https://github.com/zed-industries/agent-client-protocol/issues/new?template=05_bug_report.yml) and we will be in touch.
 - **Protocol Suggestions**: If you'd like to propose additions or changes to the protocol, please start a [discussion](https://github.com/zed-industries/agent-client-protocol/discussions/categories/protocol-suggestions) first. We want to make sure proposed suggestions align well with the project. If accepted, we can have a conversation around the implementation of these changes. Once that is complete, we will create an issue for pull requests to target.
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+### License
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+By contributing, you agree that your contributions will be licensed under the Apache 2.0 License.