Update readme to include preload usage

README.md

@@ -34,3 +34,26 @@ dotenvExpand(myEnv)
 See [test/.env](./test/.env) for examples of variable expansion in your `.env`
 file. 
 
+### Preload
+
+You can use the `--require` (`-r`) [command line option](https://nodejs.org/api/cli.html#cli_r_require_module) to preload dotenv & dotenv-extend. By doing this, you do not need to require and load dotenv or dotenv-extend in your application code. This is the preferred approach when using `import` instead of `require`.
+
+```bash
+$ node -r dotenv-extend/config your_script.js
+```
+
+The configuration options below are supported as command line arguments in the format `dotenv_config_<option>=value`
+
+```bash
+$ node -r dotenv-extend/config your_script.js dotenv_config_path=/custom/path/to/your/env/vars
+```
+
+Additionally, you can use environment variables to set configuration options. Command line arguments will precede these.
+
+```bash
+$ DOTENV_CONFIG_<OPTION>=value node -r dotenv-extend/config your_script.js
+```
+
+```bash
+$ DOTENV_CONFIG_ENCODING=latin1 node -r dotenv-extend/config your_script.js dotenv_config_path=/custom/path/to/.env
+```