resources: Recursively clone QEMU

QEMU comes with a fixed version of dtc and meson. QEMU using the
host's dtc and meson can be problematic as it could result in
a compilation error and a runtime error.

Change-Id: I8fc552fa9407dd207deb948b422981492c559ea9
Signed-off-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-resources/+/66011
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
diff --git a/src/riscv-ubuntu/README.md b/src/riscv-ubuntu/README.md
index 58f6802..9ad0c8f 100644
--- a/src/riscv-ubuntu/README.md
+++ b/src/riscv-ubuntu/README.md
@@ -51,7 +51,7 @@
 cd riscv-ubuntu/
 
 # QEMU
-git clone https://github.com/qemu/qemu
+git clone https://github.com/qemu/qemu --recursive
 cd qemu
 git checkout 0021c4765a6b83e5b09409b75d50c6caaa6971b9
 ./configure --target-list=riscv64-softmmu