add “force metafield” to docs and changelog

CHANGELOG.md

@@ -86,6 +86,7 @@ PRs are welcome! Please do open an issue to discuss first if it's a big feature,
 - [ ] webcam: Webcam modes #198
 - [ ] website: automatically generated page with all locale strings used in plugins
 - [ ] website: It would be nice in the long run to have a dynamic package builder here right on the website where you can select the plugins you need/want and it builds and downloads a minified version of them? Sort of like jQuery UI: https://jqueryui.com/download/
+- [ ] Add an option to force metafield data when uploading a file #1703
 - [ ] xhr: allow sending custom headers per file (as proposed in #785)
 - [-] dashboard: if you specified a delete endpoint, the “remove/cancel upload” button remains after the upload and it not only removes, but also sends a request to that endpoint #1216, #832 <-- not doing this anymore because https://github.com/transloadit/uppy/pull/589#issuecomment-366754294
 

website/src/docs/uppy.md

@@ -137,6 +137,8 @@ Optionally, provide rules and conditions to limit the type and/or number of file
 
 `allowedFileTypes` gets passed to the system file dialog via [`<input>`](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/file#Limiting_accepted_file_types)’s accept attribute, so only files matching these types will be selectable.
 
+> If you’d like to force a certain meta field data to be entered before the upload, you can [do so using `onBeforeUpload`](https://github.com/transloadit/uppy/issues/1703#issuecomment-507202561).
+
 ### `meta: {}`
 
 Metadata object, used for passing things like public keys, usernames, tags and so on: