docs(upsert): return value when using MySQL / MariaDB (#11093)

lib/model.js

@@ -2424,7 +2424,7 @@ class Model {
    * @param  {boolean}      [options.benchmark=false] Pass query execution time in milliseconds as second argument to logging function (options.logging).
    * @param  {boolean}      [options.benchmark=false] Pass query execution time in milliseconds as second argument to logging function (options.logging).
    * @param  {string}       [options.searchPath=DEFAULT] An optional parameter to specify the schema search_path (Postgres only)
    * @param  {string}       [options.searchPath=DEFAULT] An optional parameter to specify the schema search_path (Postgres only)
    *
    *
-   * @returns {Promise<boolean>} Returns a boolean indicating whether the row was created or updated. For Postgres/MSSQL with (options.returning=true), it returns record and created boolean with signature `<Model, created>`.
+   * @returns {Promise<boolean>} Returns a boolean indicating whether the row was created or updated. For MySQL/MariaDB, it returns `true` when inserted and `false` when updated. For Postgres/MSSQL with (options.returning=true), it returns record and created boolean with signature `<Model, created>`.
    */
    */
   static upsert(values, options) {
   static upsert(values, options) {
     options = Object.assign({
     options = Object.assign({