Updated README.md - fixed python ANTI-PATTERN in the code example

[janfilips]

Anti-pattern

The following code is a well known python anti-pattern!

wildcard import * = bad!!!

from sendgrid.helpers.mail import *

Fixes

A short description of what this PR does.

Checklist

• [x] I acknowledge that all my contributions will be made under the project's license
• [ ] I have made a material change to the repo (functionality, testing, spelling, grammar)
• [ ] I have read the Contribution Guidelines and my PR follows them
• [ ] I have titled the PR appropriately
• [ ] I have updated my branch with the main branch
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added the necessary documentation about the functionality in the appropriate .md file
• [ ] I have added inline documentation to the code I modified

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