Document SignalSourceComplex

[EthnTuttle]

I am happy to make the PR but for the function but have a question:

    pub fn new(samp_rate: Float, freq: Float, amplitude: Float) -> Self {

Context: I'm looking at a SignalSource gnu-radio block and it has 5 values:
Sample Rate: 32k
Waveform: Cosine
Frequency: 1k
Amplitude: 100m
Offest: 0

Would SignaleSourceComplex::new(32000., 1000., 100000000) be a correct translation? (i'm newer to radio so perhaps this is common knowledge?)

[ThomasHabets]

Almost. I'm pretty sure 100m here means 100 milli, or 0.1.

Pluggable waveforms and offset are not yet implemented in rustradio.

To me the names samp_rate, freq, and amplitude are self documenting. But to be beginner friendly, I'd be happy to accept documenting PRs that would help other new people in the future.