docs: add twitter link to header

[AvaGanesh]

PR Checklist

Please check if your PR fulfills the following requirements:

• [x] The commit message follows our guidelines: https://github.com/NG-ZORRO/ng-zorro-antd/blob/master/CONTRIBUTING.md#commit
• [x] Tests for the changes have been added (for bug fixes / features)
• [x] Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[x] Documentation content changes
[ ] Application (the showcase website) / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

There is no twitter/x link of the ng-zorro-antd twitter community in the official documentation

Issue Number: 5947 Issue - 5947 Adding twitter link to the header

What is the new behavior?

Added a twitter/x icon which redirects to https://twitter.com/ng_zorro

Does this PR introduce a breaking change?

[ ] Yes
[x] No

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.59%. Comparing base (a27a47e) to head (ad67830). Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8490      +/-   ##
==========================================
- Coverage   91.59%   91.59%   -0.01%     
==========================================
  Files         533      533              
  Lines       18391    18391              
  Branches     2808     2808              
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- Hits        16846    16845       -1     
- Misses       1227     1228       +1     
  Partials      318      318              

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[Laffery]

@AvaGanesh Thank you for your contribution! I'm wondering why we should put X in such an important position, what the benefit of doing so is? In fact, at the bottom of the site we have a list of links, including zorro's link in the twitter feed. I think it will be great if you would like to update this twitter link to X instead of adding it at the header:)

[AvaGanesh]

@Laffery your suggestion makes sense, I will make the changes and issue a new PR.