Docs: Make fix param clearer (fixes eslint#6366)

Updating the NodeJS API docs to avoid surprising developers when trying to use the `fix` param.

docs/developer-guide/nodejs-api.md

@@ -155,7 +155,7 @@ The `CLIEngine` is a constructor, and you can create a new instance by passing i
 * `envs` - An array of environments to load (default: empty array). Corresponds to `--env`.
 * `extensions` - An array of filename extensions that should be checked for code. The default is an array containing just `".js"`. Corresponds to `--ext`.
 * `globals` - An array of global variables to declare (default: empty array). Corresponds to `--global`.
-* `fix` - True indicates that fixes should be applied to the text when possible.
+* `fix` - True indicates that fixes should be included with the output report, and that errors and warnings should not be listed if they can be fixed. However, the files on disk will not be changed. To persist changes to disk, call [`outputFixes()`](#outputfixes).
 * `ignore` - False disables use of `.eslintignore`, `ignorePath` and `ignorePattern` (default: true). Corresponds to `--no-ignore`.
 * `ignorePath` - The ignore file to use instead of `.eslintignore` (default: null). Corresponds to `--ignore-path`.
 * `ignorePattern` - Glob patterns for paths to ignore. String or array of strings.