resources: Added information about RISCV Ubuntu boot exit

This change adds information in the riscv-ubuntu/README.md file
regarding the use of the disk image for a new riscv ubuntu
boot exit test.

Signed-off-by: Kaustav Goswami <kggoswami@ucdavis.edu>
Change-Id: I7fef429a419fbe70d516057131fa7b4eb78bfade
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-resources/+/53763
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: Bobby Bruce <bbruce@ucdavis.edu>
diff --git a/src/riscv-ubuntu/README.md b/src/riscv-ubuntu/README.md
index 8c3b018..a46bb3c 100644
--- a/src/riscv-ubuntu/README.md
+++ b/src/riscv-ubuntu/README.md
@@ -201,5 +201,6 @@
 A pre-build, gzipped, disk image is available at <http://dist.gem5.org/dist/develop/images/riscv/ubuntu-20-04/riscv-ubuntu.img.gz>. **Note**: The password set for the `ubuntu` user is `helloworld`.
 
 # Using the Disk Image
-This disk image is used in the gem5 example RISCV config, found within the gem5 repository:
-`gem5/configs/example/components-library/riscv_fs.py`.
\ No newline at end of file
+This disk image is used in the following gem5 example RISCV config files, found within the gem5 repository:
+* `gem5/configs/example/gem5_library/riscv-fs.py`, which simulates a full system running with RISCV ISA.
+* `gem5/configs/example/gem5_library/riscv-ubuntu-run.py`, which simulates a full system with RISCV based Ubuntu 20.04 disk-image. Upon successful start-up, a `m5_exit instruction encountered` is encountered. The simulation ends then.