Add doc describing CLI version marker files

lib/setup-codeql.js

@@ -65,6 +65,16 @@ function getCodeQLActionRepository(logger) {
     return util.getRequiredEnvParam("GITHUB_ACTION_REPOSITORY");
 }
 exports.getCodeQLActionRepository = getCodeQLActionRepository;
+/**
+ * CodeQL bundles are currently tagged in the form `codeql-bundle-yyyymmdd`, so it is not possible
+ * to directly find the CodeQL bundle release for a particular CLI version.
+ *
+ * To get around this, we add a `codeql-version-x.y.z.txt` asset to each bundle release that
+ * specifies the CLI version for that bundle release.
+ *
+ * In the medium term, we should migrate to a tagging scheme that allows us to directly find the
+ * CodeQL bundle release for a particular CLI version, for example `codeql-bundle-vx.y.z`.
+ */
 async function findCodeQLBundleTagDotcomOnly(cliVersion, logger) {
     logger.debug(`Trying to find the CodeQL bundle release for CLI version ${cliVersion}.`);
     const apiClient = api.getApiClient();