[lldb] Add test note

Author: da-viper

lldb/test/Shell/Commands/command-process-save-core-not-a-plugin.test

@@ -1,3 +1,6 @@
+# This checks that lldb returns an error if process save-core is called
+# with a plugin that does not exist.
+
 # RUN: %clang_host -g %S/Inputs/main.c -o %t
 # RUN: %lldb %t -s %s -o exit 2>&1 | FileCheck %s