docs: add stack exchange badge to the readme

[math411]

Issue #, if available:

Description of changes: Adds a badge for questions tagged as amazon-braket for the QC stackexchange forum.

Testing done:

Merge Checklist

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General

• [ ] I have read the CONTRIBUTING doc
• [ ] I used the commit message format described in CONTRIBUTING
• [ ] I have updated any necessary documentation, including READMEs and API docs (if appropriate)

Tests

• [ ] I have added tests that prove my fix is effective or that my feature works (if appropriate)
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[codecov[bot]]

Codecov Report

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

Project coverage is 100.00%. Comparing base (2f02107) to head (5f4acd5).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #956 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 135 135 Lines 8941 8941 Branches 2008 2008 ========================================= Hits 8941 8941 ```

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