Add Examples to `electricpy.tcycles`

[engineerjoe440]

The tcycles function is a relatively simple one, but could benefit from having examples right in the code.

It could, quite simply, be:

Examples
--------
>>> import electricpy as ep
>>> ep.tcycles(1, freq=60)
0.01666667
>>> ep.tcycles(1, freq=50)
0.02

At the same time, it would also be worth clarifying the units in which the time is returned. I seem to recall it as seconds, but may need some clarification there.