Update README and Add Pulse Width Measurement Field in Seconds (#4)

* Adding pulse width measurement in units of time to the pdw log file, previously only the pulse width was given as the number of samples in the pulse when logging.

* Update README.md with instruction to generate pulse generator heir block

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Co-authored-by: Trip Humphries <jhumphries33@jhumphries5430l.seal-ad.gtri.org>

v1.0.0 Release of gr-pdw.