Add "php bin/console assets:install" step to README installation instructions

[ethsam]

Issue Description

I suggest adding a new step in the README installation instructions for the FileManagerBundle. After installing the bundle via Composer, it is essential to run php bin/console assets:install to ensure that all assets are properly published to the public directory. This step is crucial but currently missing from the README, which might lead to confusion or improper setup for new users.

Why This Addition Is Important

The php bin/console assets:install command moves all static files from the bundle's Resources/public directory to the public directory of the Symfony application. This step is critical because it ensures that all the necessary assets (CSS, JavaScript, images, etc.) are available in the web-accessible directory, allowing FileManager to function correctly. Missing this step could prevent FileManager from displaying or functioning correctly, potentially causing a poor user experience or confusion.

Suggested README Update

I propose that the following step be added to the README under the installation section:

### Step 2: Publish Assets

After installing the bundle, you must publish the assets to the public directory. Run the following command:

```bash
php bin/console assets:install

This command will copy necessary files from the bundle's Resources/public directory to your application's public directory, ensuring that FileManager has all the assets it requires.