Fix example of Crypto::BCrypt.new(String, String, Int).

[hugopl]

Current example just doesn't work, since it expects a base64 encoded string.

[straight-shoota]

suggestion: The sample string looks like hexadecimal. Maybe we could put some other characters to clearly show that it's actually base64 encoded?

[ysbaddaden]

Every password should have a different salt so let's generate it:

Suggested change

	# password = Crypto::Bcrypt.new "secret", "0102030405060708090a0b0c0d0e0f10"
	salt = Base64.encode(Random::Secure.random_bytes(16))
	password = Crypto::Bcrypt.new "secret", salt)

[straight-shoota]

If we're generating a random salt, we would probably use the other overload with Bytes directly, without going through the base64 encoding. Or better just the .hash_secret method. Or just Bcrypt::Password.

And for individual examples, I think it's generally best to keep them short with deterministic input and output. The goal is to demonstrate the functionality of a single method.

The password itself clearly shouldn't be "secret" either. For this particular method's documentation, a string literal is fine.

We might want to enhance the documentation of BCrypt with a practical guide for end-to-end integration with production-ready examples (or not: #15276). That's out of scope here, though.