doc: add new adopters for Dragonfly

[allencloud]

Signed-off-by: Allen Sun [email protected]

Ⅰ. Describe what this PR did

According to comment dragonflyoss/dragonfly#219 (comment), we found that ChinaUnicom is using Dragonfly as well. Add it to be an adopter.

Ⅱ. Does this pull request fix one issue?

none

Ⅲ. Why don't you add test cases (unit test/integration test)? (你真的觉得不需要加测试吗？)

no need, just doc.

Ⅳ. Describe how to verify it

none

Ⅴ. Special notes for reviews

none

[codecov-io]

Codecov Report

Merging #754 into master will increase coverage by 0.16%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #754      +/-   ##
==========================================
+ Coverage   46.67%   46.84%   +0.16%     
==========================================
  Files         113      110       -3     
  Lines        6346     6321      -25     
==========================================
- Hits         2962     2961       -1     
+ Misses       3150     3125      -25     
- Partials      234      235       +1

Impacted Files	Coverage Δ
supernode/daemon/mgr/scheduler/manager.go	24.06% <0%> (-0.76%)	⬇️
client/task_info.go
client/task_delete.go
client/task_update.go
client/request.go	37.77% <0%> (+1.98%)	⬆️

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[starnop]

LGTM.