docs: Add CyberAgent to the list of Argo users

[takashabe]

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
• The title of the PR is (a) conventional, (b) states what changed, and (c) suffixes the related issues number. E.g. "fix(controller): Updates such and such. Fixes #1234". Why? for the release notes.
• Optional. I've added My organization is added to the README.
• I've signed the CLA and required builds are green.

[claassistantio]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #1926 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1926   +/-   ##
=======================================
  Coverage   10.65%   10.65%           
=======================================
  Files          35       35           
  Lines       24931    24931           
=======================================
  Hits         2657     2657           
  Misses      21935    21935           
  Partials      339      339

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 02022e4...97eeca1. Read the comment docs.

[simster7]

Thank you!