Add a parcel chapter to hello wasm-pack tutorial

[fitzgen]

I can do this once @ashleygwilliams sends me the example project that the parcel folks shared with us and let's me know when the docs are stable enough that I won't be stepping on toes and creating merge conflicts :)

TODO:

• Create a rust+parcel template in rustwasm org
• Make sure it is roughly feature complete with create-wasm-app and/or rust-webpack-template
• Add the docs to hello wasm-pack tutorial

[fitzgen]

cc @sendilkumarn

[0xcaff]

Where is this example project?