README: broken Keruyun (客如云) logo image link in "Who is using" section (404)

### Problem description

In the "Who is using" section of `README.md` (line 187), the Keruyun (客如云) logo link is broken and returns HTTP 404:

The Keruyun website has been redesigned and the old asset path no longer exists. The current official logo on https://www.keruyun.com is:

(verified: returns 200 with content-type image/svg+xml)

All other company logos in the same section were checked and work fine.

### Suggested fix

Update the broken logo URL in `README.md` to the current official logo URL.

I'm happy to submit a PR for this.

Open README.md around line 187 and inspect the Keruyun logo entry in the "Who is using" section. Replace only the broken image URL with the current official logo URL, then verify that it returns HTTP 200 with content-type image/svg+xml and that the README link renders correctly.

Written by the indexing model from the issue text.