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.