website: Updated util/m5 build instructions.

Updated util/m5 build instructions to reflect the new build targets
introduced in gem5-21.0.

Change-Id: I7921c173450ca85d44f46b183c1494120999de4b
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/43985
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: Bobby R. Bruce <bbruce@ucdavis.edu>
diff --git a/_pages/documentation/general_docs/m5ops.md b/_pages/documentation/general_docs/m5ops.md
index d5a6eaf..985a2ec 100644
--- a/_pages/documentation/general_docs/m5ops.md
+++ b/_pages/documentation/general_docs/m5ops.md
@@ -24,10 +24,13 @@
 * arm (arm-linux-gnueabihf-gcc)
 * thumb (arm-linux-gnueabihf-gcc)
 * sparc (sparc64-linux-gnu-gcc)
-* aarch64 (aarch64-linux-gnu-gcc)
+* arm64 (aarch64-linux-gnu-gcc)
+* riscv (riscv64-linux-gnu-gcc)
 
 Note if you are using a x86 system for other ISAs you need to have the cross-compiler installed. The name of the cross-compiler is shown inside the parentheses in the list above.
 
+See util/m5/README.md for more details.
+
 ## The m5 Utility (FS mode)
 
 The m5 utility (see util/m5/) can be used in FS mode to issue special instructions to trigger simulation specific functionality. It currently offers the following options: