Command-line alternative of gdnative-doc.
If you have cargo, simply run
cargo install gdnative-doc-cli
This will install gdnative-doc-cli in $CARGO_HOME/bin.
You can test it on a crate that exports gdnative structures with:
cd <path-to-my-crate>
gdnative-doc-cli --md <path-to-markdown-output>
To get more options, run gdnative-doc-cli --help.