message: docs: add export condition guide for Rollup
diff: @@ -17,7 +17,10 @@ If the target browsers for a project support ES2015+ or the bundle process suppo
  You can enable support for using the ES2015 RxJS code by configuring a bundler to use the `es2015` custom export condition during module resolution.
  Configuring a bundler to use the `es2015` custom export condition is specific to each bundler.
  If you are interested in using this option, please consult the documentation of your bundler for additional information.
  -However, some general information can be found here: https://webpack.js.org/guides/package-exports/#conditions-custom
  +However, some general information can be found here:
  +
  +- https://webpack.js.org/guides/package-exports/#conditions-custom
  +- https://github.com/rollup/plugins/blob/node-resolve-v11.0.0/packages/node-resolve/README.md#exportconditions
  To import only what you need, please {@link guide/importing#es6-via-npm check out this} guide.
  