build-5d8cd9a: update idea1.md

- add caution message
- add neopixel waveform image(wavedrom)
- add clock generation waveforma image(wavedrom)
- use standard tables instead of using pantable filter
- mention about transfer period per LED and optimum value to get 300ms/row-of-LEDs
- update counter data values for strobe generator
- 2nd simplest LFSR (>=16 bit) is 17 instead of 20
- add section to apply to 3-wire serial to Neopixel converter