stdlib,configs: Update riscvmatched-fs example docstring

This documentation string provided in the
"config/example/gem5_library/riscvmatched-fs.py" was minimal. This patch
adds more detail.

Change-Id: I0f203ea6952fc72a078594d7c30853bd426017ff
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/65851
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/65972
diff --git a/configs/example/gem5_library/riscvmatched-fs.py b/configs/example/gem5_library/riscvmatched-fs.py
index da47a4b..1ed78e8 100644
--- a/configs/example/gem5_library/riscvmatched-fs.py
+++ b/configs/example/gem5_library/riscvmatched-fs.py
@@ -25,8 +25,8 @@
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 """
-This gem5 configuration script runs a full system Ubuntu image, Linux
-kernel and calls m5 exit after the kernel is loaded.
+This gem5 configuration script runs the RISCVMatchedBoard in FS mode with a
+an Ubuntu 20.04 image and calls m5 exit after the simulation has booted the OS.
 
 Usage
 ---
@@ -34,8 +34,7 @@
 ```
 scons build/RISCV/gem5.opt
 
-./build/RISCV/gem5.opt \
-    configs/example/gem5_library/riscvmatched-fs.py
+./build/RISCV/gem5.opt configs/example/gem5_library/riscvmatched-fs.py
 ```
 """