docs: add a WIP setup doc

Signed-off-by: HaoboGu <[email protected]>

docs/src/setup_rust_environment.md

@@ -0,0 +1,13 @@
+# Setup Rust environment
+
+## Prerequisites
+
+Using RMK requires basic knowledge of programming and embedded devices. We recommend you to read [The Embedded Rust Book](https://docs.rust-embedded.org/book/) first if you're not familiar with embedded Rust.
+
+## Install Rust
+
+A Rust environment is required to use RMK. Installing Rust is easy: checkout [https://rustup.rs](https://rustup.rs), follow the instructions.
+
+## Install your target
+
+TODO