`x509-cert/test-support/Cargo.toml` sets a readme field pointing at `README.md`: https://github.com/RustCrypto/formats/blob/cb02c0f0418bf1cb133892165f9979360664eabe/x509-cert/test-support/Cargo.toml#L13 However, there is no README.md file in the x509-cert/test-support directory.
x509-cert/test-support/Cargo.tomlsets a readme field pointing atREADME.md:formats/x509-cert/test-support/Cargo.toml
Line 13 in cb02c0f
However, there is no README.md file in the x509-cert/test-support directory.