README: don't ask user to manually add "avanzu/admin-theme-bundle": "~1.3" to composer.json
README: don't ask user to manually add "avanzu/admin-theme-bundle": "~1.3" to composer.json

Running "php composer.phar require avanzu/admin-theme-bundle" will actually add this line to composer.json file

avanzu/AdminThemeBundle,avanzu/AdminThemeBundle