improve README.md thanks section

[zhoney]

Change-Id: Ie83d64d1dad57e896356f8abd2f853b8979351ed

[codecov]

Codecov Report

Merging #548 into master will increase coverage by 0.02%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #548      +/-   ##
============================================
+ Coverage     70.06%   70.08%   +0.02%     
- Complexity     3412     3414       +2     
============================================
  Files           216      216              
  Lines         16516    16516              
  Branches       2361     2361              
============================================
+ Hits          11572    11576       +4     
+ Misses         3687     3682       -5     
- Partials       1257     1258       +1

Impacted Files	Coverage Δ	Complexity Δ
...va/com/baidu/hugegraph/backend/cache/RamCache.java	72.54% <0%> (+0.39%)	45% <0%> (+1%)	⬆️
...c/main/java/com/baidu/hugegraph/util/JsonUtil.java	58.49% <0%> (+5.66%)	5% <0%> (+1%)	⬆️

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