Add a link for the the 433MHz variant of the Feather M0 RFM69

[FoamyGuy]

Currently there is only a link for the 868 / 915 MHz version listed on the download page for this device.

However the same download applies to the 433 MHz version as well. Adding a link to the 433 MHz version and making a note on which link is which will help confirm for users with the 433 device that they are on the right page for updating Circuit Python version.

This is the md file where this change would need to take place: https://github.com/adafruit/circuitpython-org/blob/master/_board/feather_m0_rfm69.md