chore(readme): Adding pinot logo into Readme Supported Databases Section

[xiangfu0]

SUMMARY

Adding pinot logo into Readme Supported Databases Section

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

You can preview it from here:
https://github.com/xiangfu0/superset/tree/pinot-logo#supported-databases

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #18798 (b9b2eec) into master (2d67d2f) will increase coverage by 0.02%.
The diff coverage is 60.00%.

❗ Current head b9b2eec differs from pull request most recent head 23cd335. Consider uploading reports for the commit 23cd335 to get more accurate results

@@            Coverage Diff             @@
##           master   #18798      +/-   ##
==========================================
+ Coverage   66.32%   66.34%   +0.02%     
==========================================
  Files        1620     1620              
  Lines       63087    63088       +1     
  Branches     6372     6372              
==========================================
+ Hits        41840    41857      +17     
+ Misses      19590    19570      -20     
- Partials     1657     1661       +4     

Flag	Coverage Δ
javascript	51.30% <33.33%> (+0.04%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...frontend/src/SqlLab/components/ResultSet/index.tsx	50.73% <ø> (ø)
...lLab/components/ExploreCtasResultsButton/index.tsx	8.33% <33.33%> (ø)
superset/reports/notifications/slack.py	87.67% <100.00%> (+0.34%)	⬆️
...board/components/nativeFilters/FilterBar/index.tsx	80.17% <0.00%> (+10.34%)	⬆️
...rd/components/nativeFilters/FilterBar/keyValue.tsx	45.45% <0.00%> (+27.27%)	⬆️

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[zhaoyongjie]

LGTM