bricks/virtualhub/README: Install prerequisites.

laurensvalk · laurensvalk · commit 38e6c1f2aa3f · 2023-11-16T08:39:49.000+01:00
diff --git a/bricks/virtualhub/README.md b/bricks/virtualhub/README.md
@@ -7,6 +7,10 @@ and creating virtual robots in a 3-D environment.
 
 ## Building
 
+Prerequisites:
+
+    make -C micropython/ports/unix submodules
+
 Run:
 
     make virtualhub
