docs(@angular/cli): Add update guide link to the 'Update" section (#5878)

Author: kirjs

README.md

@@ -117,6 +117,8 @@ npm install --save-dev @angular/cli@latest
 npm install
 ```
 
+If you are updating to 1.0 from a beta or RC version, check out our [1.0 Update Guide](https://github.com/angular/angular-cli/wiki/stories-1.0-update).
+
 You can find more details about changes between versions in [CHANGELOG.md](https://github.com/angular/angular-cli/blob/master/CHANGELOG.md).