Add note about install-jsdeps.sh to upgrade procedure

UPGRADING

@@ -41,15 +41,18 @@ it on a unix system, you need to do the following operations by hand:
    ./skins/
    ./plugins/
    ./vendor/
+4. Update dependencies:
 4a. If you previously installed plugins through composer, update dependencies
-   by running `php composer.phar update --no-dev`
+   by running `php composer.phar update --no-dev`.
 4b. Install/update dependencies using composer:
    - get composer from https://getcomposer.org/download/
    - rename the composer.json-dist file into composer.json
    - if you want to use LDAP address books, enable the LDAP libraries in your
      composer.json file by moving the items from "suggest" to the "require"
      section (remove the explanation texts after the version!).
-   - run `php composer.phar install --no-dev`
+   - run `php composer.phar install --no-dev`.
+4c. If you use git sources or the release package without dependencies
+   update javascript dependencies by executing `bin/install-jsdeps.sh` script.
 5. Run `./bin/update.sh` from the commandline OR
    open http://url-to-roundcube/installer/ in a browser and choose "3 Test config".
    To enable the latter one, you have to temporary set 'enable_installer'