chore: update readme to contain propagate framework errors cli option

Author: gregorygaines

README.md

@@ -183,6 +183,7 @@ ignored.
 | `--source`         | `FUNCTION_SOURCE`         | The path to the directory of your function. Default: `cwd` (the current working directory)                                                                                                                       |
 | `--log-execution-id`| `LOG_EXECUTION_ID`        | Enables execution IDs in logs, either `true` or `false`. When not specified, default to disable. Requires Node.js 13.0.0 or later.                                                                                |
 | `--ignored-routes`| `IGNORED_ROUTES`        | A route expression for requests that should not be routed the function. An empty 404 response will be returned. This is set to `/favicon.ico|/robots.txt` by default for `http` functions.                                                     |
+| `--propagate-framework-errors` | `PROPAGATE_FRAMEWORK_ERRORS` | Enables propagating framework errors to the client application error handler, either `true` or `false`. When not specified, default to disable.|
 
 You can set command-line flags in your `package.json` via the `start` script.
 For example: