fix(docs): Correct deadline example in README

[TadejPolajnar]

The example the README was generating deadline as a floating-point number, which causes an Invalid input: query.deadline: Expected integer, received float error from the endpoint.

This PR corrects the example by using Math.floor() to ensure the deadline is always an integer.

Before:

const deadline = String(Date.now() / 1000 + 10 * 60) // 1750647648.403

Aftee:

const deadline = String(Math.floor(Date.now() / 1000) + 10 * 60) // 1750647648

[dglowinski]

Well spotted, thanks!