provide better snippet for secret token generation

[beniwohli]

What does this pull request do?

While the previous snippet wasn't necessarily bad, it used
uuid4 for something it isn't intended to. Python 3 provides
a cryptographically secure token generator, so let's tell
our users to use that instead.

[ghost]

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• Start Time: 2022-06-21T07:07:43.340+0000

• Duration: 3 min 8 sec

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