Update tail-based-sampling.md

[endorama]

A minor change to the data type for sample_rate. We mention that

The sample rate must be greater than or equal to 0 and less than or equal to 1.

which if restricted to an int type would only allow 0 and 1. A more reasonable (unless there is a reason not clear to me) data type here would be float, allowing any decimal precision value, like the 0.01 mentioned as example.