radicle: add .external_template(false) to libgit2 call — heartwood

Without this, rad clone fails with: Error: checkout: git: failed to initialize repository with template ‘hooks/README.sample’: Permission denied; class=Os (2)

     let project = doc.project()?;
     let mut opts = git2::RepositoryInitOptions::new();
     opts.no_reinit(true).description(project.description());
     opts.no_reinit(true).description(project.description()).external_template(false);
     let repo = git2::Repository::init_opts(path.as_ref(), &opts)?;
     let url = git::Url::from(proj);