docs(FAQ): improve issue about Basic auth and 401 status code (#266)

fixes #266

CONTRIBUTORS.md

@@ -36,4 +36,6 @@
 - Ben Jackson [@bjj](https://github.com/bjj)
 - 三十文 [@xfduan](https://github.com/xfduan)
 - Aram Akhavan [@kaysond](https://github.com/kaysond)
-- Jason Tackaberry [@jtackaberry](https://github.com/jtackaberry)
+- Jason Tackaberry [@jtackaberry](https://github.com/jtackaberry)
+- Maxime Loliée [@loliee](https://github.com/loliee)
+- Enrico [@Enrico204](https://github.com/Enrico204)

README.md

@@ -75,8 +75,8 @@ If you like my work and want to support it, don't hesitate to [sponsor me](https
     -   This means you are using a UI with HTTPS and your registry is using HTTP (unsecured). When you are on a HTTPS site, you can't get HTTP content. Upgrade you registry with a HTTPS connection.
 -   Why the default nginx `Host` is set to `$http_host` ?
     -   This fixes the issue [#88](https://github.com/Joxit/docker-registry-ui/issues/88). More about this in [#113](https://github.com/Joxit/docker-registry-ui/issues/113).
--   Why DELETE fails with 401 status code (using Basic Auth) ?
-    -   This is caused by a bug in docker registry, I suggest to have your UI on the same domain than your registry and use `NGINX_PROXY_PASS_URL` e.g. registry.example.com/ui/. (see [#104](https://github.com/Joxit/docker-registry-ui/issues/104), [#204](https://github.com/Joxit/docker-registry-ui/issues/204), [#207](https://github.com/Joxit/docker-registry-ui/issues/207), [#214](https://github.com/Joxit/docker-registry-ui/issues/214)).
+-   Why OPTIONS (aka preflight requests) and DELETE fails with 401 status code (using Basic Auth) ?
+    -   This is caused by a bug in docker registry, it returns 401 status requests on preflight requests, this breaks [W3C preflight-request specification](https://www.w3.org/TR/cors/#preflight-request). I suggest to have your UI on the same domain than your registry e.g. registry.example.com/ui/ **or** use `NGINX_PROXY_PASS_URL` **or** configure a nginx/apache/haproxy in front of your registry that returns 200 on each OPTIONS requests. (see [#104](https://github.com/Joxit/docker-registry-ui/issues/104), [#204](https://github.com/Joxit/docker-registry-ui/issues/204), [#207](https://github.com/Joxit/docker-registry-ui/issues/207), [#214](https://github.com/Joxit/docker-registry-ui/issues/214), [#266](https://github.com/Joxit/docker-registry-ui/issues/266)).
 -   Can I use the docker registry ui as a standalone application (with Electron) ?
     -   Yes, check out the example [here](https://github.com/Joxit/docker-registry-ui/tree/main/examples/electron). (see [#129](https://github.com/Joxit/docker-registry-ui/pull/129))
 -   I deleted images through the UI, but they are still present on the server. How can I delete them?