Format build provenance attestation section

README.md

@@ -37,6 +37,9 @@ To build an XCFramework for macOS and iOS, run the following:
 
 Download the binary from [releases](https://github.com/blechschmidt/tun2proxy/releases) and put it in your `PATH`.
 
+<details>
+  <summary>Authenticity Verification</summary>
+
 Since v0.2.23 [build provenance attestations](https://docs.github.com/en/actions/security-guides/using-artifact-attestations-to-establish-provenance-for-builds#verifying-artifact-attestations-with-the-github-cli)
 are supported. These allow you to ensure that the builds have been generated from the code on GitHub through the GitHub
 CI/CD pipeline. To verify the authenticity of the build files, you can use the [GitHub CLI](https://cli.github.com/):
@@ -44,6 +47,8 @@ CI/CD pipeline. To verify the authenticity of the build files, you can use the [
 gh attestation verify <*.zip file> --owner tun2proxy
 ```
 
+</details>
+
 ### Install from source
 
 If you have [rust](https://rustup.rs/) toolchain installed, this should work: