message: feat(readme): update desc to make it clearer that publishing is optional
diff: This tool seeks to be a one-stop shop for building and working with rust-
  generated WebAssembly that you would like to interop with JavaScript, in the
  -browser or with Node.js. `wasm-pack` helps you build and publish rust-generated
  -WebAssembly to the npm registry to be used alongside any other javascript
  -package in workflows that you already use, such as [webpack] or [greenkeeper].
  +browser or with Node.js. `wasm-pack` helps you build rust-generated
  +WebAssembly packages that you could publish to the npm registry, or otherwise use
  +alongside any javascript packages in workflows that you already use, such as [webpack]
  +or [greenkeeper].
  [bundler-support]: https://github.com/rustwasm/team/blob/master/goals/bundler-integration.md#details
  [webpack]: https://webpack.js.org/
  