docs: recommend 2GB of RAM for Viewperf tests

docs/viewperf.html

@@ -32,6 +32,10 @@ These issues have been reported to the SPEC organization in the hope that
 they'll be fixed in the future.
 </p>
 
+<p>
+Some of the Viewperf tests use a lot of memory.
+At least 2GB of RAM is recommended.
+</p>
 
 
 <h2>Catia-03 test 2</h2>