message: add note on overriding global alloc
diff: @@ -21,6 +21,8 @@ use casper_node::{
  };
  use prometheus::Registry;
  +// We override the standard allocator to gather metrics and tune the allocator via th MALLOC_CONF
  +// env var.
  #[global_allocator]
  static ALLOC: jemallocator::Jemalloc = jemallocator::Jemalloc;
  