docs: clarified breaking changes

UPGRADING.md

@@ -3,12 +3,11 @@
 
 ## Upgrading from v8 to v9
 
-**There are four major breaking changes:**
+**There are three major breaking changes:**
 
 1. The usage of `bree.start()` and `bree.run()` methods must be changed to `await bree.start()` or `await bree.run()` (see the example below).
-2. Passing a custom value for the `root` option with a file's path must be changed to include the file's extension.  For example, an option of `root: '/path/to/dir/index'` must be changed to `root: '/path/to/dir/index.js`.
-3. The usage of `bree.add()` must be changed to `await bree.add()` (since we now have asynchronous job validation and loading).
-4. We have opted for `util.debuglog` as opposed to the userland `debug` package for debug logging.  This means you must run `NODE_DEBUG=bree node app.js` as opposed to `DEBUG=bree node app.js`.
+2. The usage of `bree.add()` must be changed to `await bree.add()` (since we now have asynchronous job validation and loading).
+3. We have opted for `util.debuglog` as opposed to the userland `debug` package for debug logging.  This means you must run `NODE_DEBUG=bree node app.js` as opposed to `DEBUG=bree node app.js`.
 
 Here is a complete list of the underlying changes made:
 
@@ -44,7 +43,7 @@ Here is a complete list of the underlying changes made:
   * However we have dummy-proofed this new approach, and `bree.init()` will be invoked (if and only if it has not yet been invoked successfully) when you call `bree.start()` (or any similar method that accesses `this.config.jobs` internally).
   * Internal methods such as `validate` exported by `src/job-validator.js` are now asynchronous and return Promises (you do not need to worry about this unless you're doing something custom with these functions).
 
-* The default `root` option has been changed from `resolve('jobs')` to ``resolve(`jobs/index.${config.defaultExtension}`)`` (the default value for `config.defaultExtension` is `"js"`).  You may need to change this or the value for `defaultExtension` entirely if you are using `.mjs` extension on the file name in your root directory (only applicable if you use this option and do not have it set to `false`).
+* The default `root` option will now attempt to resolve an absolute file path for an index since we are using dynamic imports.  If you are using `index.mjs` (as opposed to `index.js` then you will need to set a value for the option `defaultRootIndex`).
 
 * The method `add()` is now a Promise (you should call `await bree.add(jobs)`.
 
@@ -54,8 +53,6 @@ Here is a complete list of the underlying changes made:
 
 * We've also refactored synchronous methods such as `fs.statSync` to `fs.promises.stat` and made job validation asynchronous.
 
-* Since we use `await import(...)` and use dynamic imports (as opposed to v8 behavior which was to use `require`), we will automatically fetch the `root` directory file for a file of `defaultRootIndex` (this is configurable, see the new option added).
-
 * Plugins that extend `bree.init()` may need rewritten, as `bree.init()` is now a Promise.
 
 * If you are on Node version <= v12.20.0, please upgrade to the latest Node v12, but preferably please upgrade to the latest Node LTS (at the time of this writing it is Node v16, but if you can't upgrade to Node v16, at least upgrade to Node v14).  Node v12 is EOL as of April 2022.