docs(readme): hint to where to get the file sources

Author: tabcat

readme.md

@@ -16,6 +16,8 @@ source: [./example](https://github.com/cypsela/browser-source/tree/master/exampl
 
 Api docs: [cypsela.github.io/browser-source](https://cypsela.github.io/browser-source)
 
+Instances of these data types are available from [\<input />](https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/input) elements, [drag-and-drop events](https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement/drop_event), and window methods like [showOpenFilePicker](https://developer.mozilla.org/en-US/docs/Web/API/Window/showOpenFilePicker).
+
 ### [FileList](https://developer.mozilla.org/docs/Web/API/FileList) Source
 
 ```ts
@@ -56,7 +58,7 @@ import { unixfs } from '@helia/unixfs'
 const helia = await createHelia()
 const fs = unixfs(helia)
 
-const handle: FileSystemHandle = /* Get from drag-and-drop events */;
+const handle: FileSystemHandle = /* Get from drag-and-drop events and window.showOpenFilePicker */;
 
 for await (const _ of fs.addAll(fsHandleSource(handle))) {}
 ```