Refine the build instructions about JIT compilation

Author: jserv

README.md

@@ -40,17 +40,26 @@ and [SDL2_Mixer library](https://wiki.libsdl.org/SDL2_mixer) installed.
 * macOS: `brew install sdl2 sdl2_mixer`
 * Ubuntu Linux / Debian: `sudo apt install libsdl2-dev libsdl2-mixer-dev`
 
-### JIT compiler
-The tier-2 JIT compiler in `rv32emu` leverages LLVM for powerful optimization. Therefore, the target system must have [`LLVM`](https://llvm.org/) installed, with version 17 recommended. If `LLVM` is not installed, only the tier-1 JIT compiler will be used for performance enhancement.
+### Experimental JIT compilation
+The tier-2 JIT compiler in `rv32emu` leverages LLVM for powerful optimization.
+Therefore, the target system must have [`LLVM`](https://llvm.org/) installed, with version 17 recommended.
+If `LLVM` is not installed, only the tier-1 JIT compiler will be used for performance enhancement.
 
 * macOS: `brew install llvm@17`
 * Ubuntu Linux / Debian: `sudo apt-get install llvm-17`
 
-Build the emulator.
+Build the emulator with experimental JIT compiler:
+```shell
+$ make ENABLE_JIT=1
+```
+
+If you don't want the JIT compilation feature, simply build with the following:
 ```shell
 $ make
 ```
 
+### Verify with prebuilt RISC-V ELF files
+
 Run sample RV32I[M] programs:
 ```shell
 $ make check