Add upgrade notes to README.

Author: chriskrycho

README.md

@@ -25,6 +25,12 @@ In addition to ember-cli-typescript, the following are installed:
 - Files:
     + [`tsconfig.json`](https://www.typescriptlang.org/docs/handbook/tsconfig-json.html)
 
+### Upgrading
+
+1. Update `package.json` for `ember-cli-typescript` to `^1.0.0`.
+2. Run `yarn` or `npm install`.
+3. Run `ember g ember-cli-tylescript` to update the generated files (`tsconfig.json` in particular), and review the changes before committing. If you've made specific customizations, you may want to merge them; see the [Notes on `tsconfig.json`](https://github.com/typed-ember/ember-cli-typescript/tree/v1.0.0#notes-on-tsconfigjson) in the README.
+
 
 ## Notes on `tsconfig.json`