This diagram uses the original Gemma but you can also use the Gemma M0 with the exact same wiring!
Above is the circuit diagram for the simple tiara. All ground pads are connected to GND on GEMMA, likewise all power pads are connected to Vout on GEMMA, and data lines are chained from D1 to the inward facing arrow on the first pixel, then from each pixel's outward facing arrow to the next pixel's inward facing arrow.
Get creative with your tiara design! This one uses a NeoPixel ring in the center, and the wiring is barely different than above.