Create documentation about ARM architecture

I strongly believe it is important to cover the ARM architecture because it is widely used in modern embedded systems, STM32 and Raspberry pi boards are built around ARM-based CPU cores, and it's highly relevant for understanding low-level programming for embedded devices.

I’d like to take this issue and work on it.

The issue names no documentation file, test, or entry point. Start by locating the repository’s existing documentation structure and ARM-related material, then define the scope around ARM, STM32, and Raspberry Pi. Done means the documentation covers ARM architecture in the context of embedded systems and low-level programming.

Written by the indexing model from the issue text.