feat: add mention of possibility of perhaps async in the file() loader

src/content/docs/en/guides/content-collections.mdx

@@ -90,7 +90,7 @@ Astro provides [two built-in loader functions](/en/reference/content-loader-refe
 
 The [`glob()` loader](/en/reference/content-loader-reference/#glob-loader) creates entries from directories of Markdown, MDX, Markdoc, JSON, YAML, or TOML files from anywhere on the filesystem. It accepts a `pattern` of entry files to match using glob patterns supported by [micromatch](https://github.com/micromatch/micromatch#matching-features), and a base file path of where your files are located. Each entry's `id` will be automatically generated from its file name. Use this loader when you have one file per entry.
 
-The [`file()` loader](/en/reference/content-loader-reference/#file-loader) creates multiple entries from a single local file. Each entry in the file must have a unique `id` key property. It accepts a `base` file path to your file and optionally a [`parser` function](#parser-function) for data files it cannot parse automatically. Use this loader when your data file can be parsed as an array of objects.
+The [`file()` loader](/en/reference/content-loader-reference/#file-loader) creates multiple entries from a single local file. Each entry in the file must have a unique `id` key property. It accepts a `base` file path to your file and optionally a [`parser` function](#parser-function) for data files it cannot parse automatically, or to parse data asynchronously. Use this loader when your data file can be parsed as an array of objects.
 
 ```ts  title="src/content.config.ts" {6,10}
 import { defineCollection } from 'astro:content';

src/content/docs/en/reference/content-loader-reference.mdx

@@ -172,7 +172,7 @@ An optional object with the following properties:
 
 <p>
 
-**Type:** `(text: string) => Record<string, Record<string, unknown>> | Array<Record<string, unknown>>`
+**Type:** `(text: string) => Record<string, Record<string, unknown>> | Array<Record<string, unknown>> | Promise<Record<string, Record<string, unknown>> | Array<Record<string, unknown>>>`
 </p>
 
 A callback function to create a collection from a file’s contents. Use it when you need to process file not supported by default (e.g. `.csv`) or when using [nested `.json` documents](/en/guides/content-collections/#nested-json-documents).