Update README for Docker image artifacts

Document how to fetch and run user-mode and system-mode artifacts
from the rv32emu-prebuilt repository when using the Docker image.

Link: https://github.com/sysprog21/rv32emu-prebuilt

Author: kaiii708

README.md

@@ -143,6 +143,40 @@ The usage and limitations of Doom and Quake demo are listed in [docs/demo.md](do
 ### Docker image
 The image containing all the necessary tools for development and testing can be executed by `docker run -it sysprog21/rv32emu:latest`. It works for both x86-64 and aarch64 (e.g., Apple's M1 chip) machines.
 
+To keep the Docker image minimal, executables and prebuilt images are not embedded. Follow the steps below to fetch the required artifacts.
+
+##### User-Mode
+Fetch and extract the latest prebuilt user-mode ELF artifacts:
+```shell
+$ wget $(wget -qO- 'https://api.github.com/repos/sysprog21/rv32emu-prebuilt/releases?per_page=100' \
+  | grep browser_download_url | grep ELF | head -n 1 | cut -d '"' -f4)
+
+$ tar -xzvf rv32emu-prebuilt.tar.gz
+```
+To run `rv32emu-user`, consider the following examples:
+```shell
+# Run a local ELF program
+build/rv32emu-user build/hello.elf
+
+# Run a prebuilt user-mode program (e.g., pi)
+build/rv32emu-user rv32emu-prebuilt/riscv32/pi
+```
+
+##### System-Mode
+Fetch and extract the latest prebuilt system-mode Linux image artifacts:
+```shell
+$ wget $(wget -qO- 'https://api.github.com/repos/sysprog21/rv32emu-prebuilt/releases?per_page=100' \
+  | grep browser_download_url | grep Linux-Image | head -n 1 | cut -d '"' -f4)
+
+$ tar -xzvf rv32emu-linux-image-prebuilt.tar.gz
+```
+To run `rv32emu-system`, use the following:
+```shell
+$ build/rv32emu-system \
+  -k rv32emu-linux-image-prebuilt/linux-image/Image \
+  -i rv32emu-linux-image-prebuilt/linux-image/rootfs.cpio
+```
+
 ### Customization
 `rv32emu` is configurable, and you can override the below variable(s) to fit your expectations:
 * `ENABLE_RV32E`: RV32E Base Integer Instruction Set