Function build_concept 

pub fn build_concept(
    type_: &str,
    title: &str,
    description: Option<&str>,
    tags: &[String],
    timestamp: &str,
    body: Option<&str>,
) -> String

Build a new concept’s file text: a frontmatter block (a non-empty type is required by OKF) followed by the body, defaulting to a single # title heading when no body is given.