Added readme information about performance testing.
Added readme information about performance testing.

WebAssembly/wasm-to-llvm-prototype,mildred/wasm-to-llvm-prototype,mildred/wasm-to-llvm-prototype,WebAssembly/wasm-to-llvm-prototype,WebAssembly/wasm-to-llvm-prototype,mildred/wasm-to-llvm-prototype