staging: pi433: Added information about bit_rate configuration

Information in the TODO file for bit_rate configuration is
insufficient.

This patch adds information on how to approach when considering
to modify bit_rate to support upto 300kbps.

Signed-off-by: Guru Mehar Rachaputi <gurumeharrachaputi@gmail.com>
Acked-by: Dan Carpenter <error27@gmail.com>
Link: https://lore.kernel.org/r/Y9laj+z0TuasBRx5@combine-ThinkPad-S1-Yoga


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>