Update README to include ffmpeg

README.md

@@ -85,6 +85,8 @@ Before the project can be built, you must first install the [.NET 5.0 SDK](https
 
 Instructions to run this project from the command line are included here, but you will also need to install an IDE if you want to debug the server while it is running. Any IDE that supports .NET Core development will work, but two options are recent versions of [Visual Studio](https://visualstudio.microsoft.com/downloads/) (at least 2017) and [Visual Studio Code](https://code.visualstudio.com/Download).
 
+[ffmpeg](https://ffmpeg.org/download.html) will also need to be installed.
+
 ### Cloning the Repository
 
 After dependencies are installed you will need to clone a local copy of this repository. If you just want to run the server from source you can clone this repository directly, but if you are intending to contribute code changes to the project, you should [set up your own fork](https://jellyfin.org/docs/general/contributing/development.html#set-up-your-copy-of-the-repo) of the repository. The following example shows how you can clone the repository directly over HTTPS.