Add webinar banner to README

[meili-bot]

This PR is auto-generated.

Update README.md with Webinar Banner.

[codecov[bot]]

Codecov Report

All modified lines are covered by tests :white_check_mark:

Comparison is base (a1ed92c) 82.03% compared to head (196c850) 82.03%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #362 +/- ## ======================================= Coverage 82.03% 82.03% ======================================= Files 57 57 Lines 1353 1353 ======================================= Hits 1110 1110 Misses 243 243 ```

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[meili-bors[bot]]

Build succeeded:

• integration-tests (dart 3.0.0)
• linter-check
• pana