UX: Add alert about users not being able to upload screenshots/videos

Add alert that informs the user that they're not able to upload videos or pictures, but instead they have to fill in a filepath to a screenshots or video in the repository of the code.

An alert could look like this:

In markdown it could look like this:

```
:::info[Input values for **screenshots** and **videos** should be static filepaths]

Since this tool generates a `publiccode.yml` file without access to your Git repository, please enter static filepaths for screenshots and videos (e.g., `'/path/to/screenshot.png'`).

:::
```