Add BingX

[brklyn8900]

Resolves #88

Brief description

This PR adds BingX to the list of exchanges in the section Where to get KOIN of the landing page.

Checklist

• [x] I have built this pull request locally
• [ ] I have ran the unit tests locally
• [x] I have manually tested this pull request
• [x] I have reviewed my pull request
• [ ] I have added any relevant tests

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