Make equation in waveform generation easier to read

[rtoy]

Describe the issue

The equation for waveform generation is hard to read because the first set of brackets within the summation is small.

Where Is It

See https://webaudio.github.io/web-audio-api/#waveform-generation

Additional Information

It would be better if had large parens, like in the equation in https://webaudio.github.io/web-audio-api/#waveform-normalization which is basically the same equation.

[rtoy]

Using left( to have a larger open paren doesn't really make it any larger since the equation itself isn't very tall. Just leave it.