Improve Timeout.timeout documentation formatting and typos

[ybiquitous]

This PR makes a few minor improvements to the documentation of the Timeout.timeout method. The changes include fixing typos and enhancing formatting for better readability.

We can see the latest version of the documentation here:
https://docs.ruby-lang.org/en/master/Timeout.html#method-c-timeout

Also, we can verify this change locally by running:

rdoc
open doc/Timeout.html