Rust: Restore some documentation.

Author: geoffw0

rust/ql/lib/codeql/rust/Concepts.qll

@@ -25,6 +25,10 @@ module ThreatModelSource {
   abstract class Range extends DataFlow::Node {
     /**
      * Gets a string that represents the source kind with respect to threat modeling.
+     *
+     * See
+     * - https://github.com/github/codeql/blob/main/docs/codeql/reusables/threat-model-description.rst
+     * - https://github.com/github/codeql/blob/main/shared/threat-models/ext/threat-model-grouping.model.yml
      */
     abstract string getThreatModel();