add doc to pg_test module in template
Document that the `pg_test` module generated by the `cargo pgx new` template is a required item for a pgx extension if users ever want to use `cargo pgx test`.
@@ -19,6 +19,8 @@ mod tests {{
}}
+/// This module is required by `cargo pgx test` invocations.
+/// It must be visible at the root of your extension crate.
#[cfg(test)]
pub mod pg_test {{
pub fn setup(_options: Vec<&str>) {{
