Update Pico 2 build instructions

README.md

diff --git a/README.md b/README.md
index 32802b2..bfdb821 100644
--- a/README.md
+++ b/README.md
@@ -57,7 +57,7 @@
 
 ```
 git submodule sync
-git submodule update --init
+git submodule update --init --recursive
 mkdir build-pico2
 cd build-pico2
 cmake -DDEBUG_ON_PICO=1 -DPICO_BOARD=pico2 -DPICO_PLATFORM=rp2350 ../