create upgrade guide

Author: nklayman

UPGRADING.md

@@ -0,0 +1,22 @@
+# Upgrading
+
+**Note: This guide is for upgrading from <=v0.3.2 to >=v1.0.0.**
+
+## Steps:
+
+ 1. Re-invoke the generator for vue-cli-plugin-electron-builder by running `vue invoke electron-builder`. Make sure to update the package before running.
+ 2. You may delete `src/main/index.js`. If you have modified it, those modifications must be moved to `src/background.js` after re-invoking the generator.
+ 3. You may delete any electron-webpack config options, they will not be used. By default, they are in `package.json` under `electronWebpack`.
+ 4. You may delete any electron-builderconfig options, they will not be used. By default, they are in `package.json` under `build`. Any changes that you have made to these must be [moved to plugin options](https://github.com/nklayman/vue-cli-plugin-electron-builder/blob/v1-dev/README.md#configuring-electron-builder).
+ 5. You may remove `webpackConfig` and `webpackMainConfig` from vue-cli-plugin-electron-builder's plugin options. Webpack config for the renderer process is your normal webpack config, and you can use the `chainWebpackMainProcess` function ([guide](https://github.com/nklayman/vue-cli-plugin-electron-builder/blob/v1-dev/README.md#webpack-configuration)).
+ 6. You may remove `electron-webpack`, `electron-builder`, and, if used, `electron-webpack-ts` from your devDependencies. You may also remove  `source-map-support` from your dependencies.
+
+## What has changed:
+
+ - Electron-webpack is no longer used. Instead, your app is built as normal (but with some slight configuration changes).
+ - This means there is no need to change your config to work with stylus, sass, or any other special files.
+ - Typescript support is [automatic](https://github.com/nklayman/vue-cli-plugin-electron-builder/blob/v1-dev/README.md#adding-typescript-support) for both processes, just add the `@vue/typescript` plugin.
+ - Your normal build will not be overwritten by `build:electron`.
+ - The [folder structure](https://github.com/nklayman/vue-cli-plugin-electron-builder/blob/v1-dev/README.md#folder-structure) has changed dramatically.
+ - Electron-builder's [config](https://github.com/nklayman/vue-cli-plugin-electron-builder/blob/v1-dev/README.md#configuring-electron-builder) is now taken from the `builderConfig` key in vue-cli-plugin-electron-builder's plugin options.
+ - To learn more about the internals of this plugin, see [how it works](https://github.com/nklayman/vue-cli-plugin-electron-builder/blob/v1-dev/README.md#how-it-works).