fix(init): adds a comment to the generated EHR 'mainFields' option

- only for commonjs/ non 'type: module' repos

- telling how to put into that field when migrating to ESM (or being on ESM, without having 'type: module' in package.json (which _is_ totally possible)

src/cli/init-config/build-config.mjs

@@ -138,7 +138,11 @@ function buildMainFieldsAttribute(pInitOptions) {
  if (pInitOptions.isTypeModule) {
  return `mainFields: ["module", "main", "types", "typings"],`;
  }
- return `mainFields: ["main", "types", "typings"],`;
+ return `
+ // if you migrate to ESM (or are in an ESM environment already) you will want to
+ // have "module" in the list of mainFields, like so:
+ // mainFields: ["module", "main", "types", "typings"],
+ mainFields: ["main", "types", "typings"],`;
 }
 
 /**