Add mention of PICO_PLATFORM=rp2350-arm-ns to README
diff --git a/src/rp2350/README.md b/src/rp2350/README.md
index 528d193..6dacfa8 100644
--- a/src/rp2350/README.md
+++ b/src/rp2350/README.md
@@ -1,5 +1,5 @@
This directory contains files specific to the RP2350 hardware. It is only used when building for RP2350 platforms, i.e.
-`PICO_PLATFORM=rp2350-arm-s` or `PICO_PLATFORM=rp2350-riscv`
+`PICO_PLATFORM=rp2350-arm-s`, `PICO_PLATFORM=rp2350-arm-ns` or `PICO_PLATFORM=rp2350-riscv`
`hardware_regs` contains low level hardware register #defines autogenerated from the RP2350 chip definition itself.