minor #983 Add development section to explain working with assets (bocharsky-bw)

This PR was merged into the master branch.

Discussion
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Add development section to explain working with assets

Add a few words about how to work with assets in Symfony Demo, basically to help with questions like #980

Commits
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d52a4dd Add development section to explain working with assets

Author: javiereguiluz

README.md

@@ -42,6 +42,22 @@ If you don't have the Symfony client installed, run `php bin/console server:run`
 Alternatively, you can [configure a web server][3] like Nginx or Apache to run
 the application.
 
+Development
+-----------
+
+This project uses Yarn package manager for managing JavaScript dependencies along
+with [Webpack Encore][5] library that helps working with CSS and JavaScript files
+that are stored in `assets/` directory . Every time you make any change in those
+files - you will need to rebuild assets. For this, just execute:
+
+```bash
+$ yarn install
+$ yarn build
+```
+
+During the development, instead of `yarn build` you may want to run `yarn watch` which
+will watch for any changes in `assets/` and rebuild assets for you automatically.
+
 Tests
 -----
 
@@ -56,3 +72,4 @@ $ ./bin/phpunit
 [2]: https://symfony.com/doc/current/reference/requirements.html
 [3]: https://symfony.com/doc/current/cookbook/configuration/web_server_configuration.html
 [4]: https://symfony.com/download
+[5]: https://github.com/symfony/webpack-encore