README.md: add GStreamer library dependency information

README.md

@@ -11,7 +11,9 @@ PackSquash analyzes all the resource pack files in a directory, applying file ty
 In addition to these techniques, all files are compressed in the generated ZIP file using the Zopfli algorithm, which is a state of the art DEFLATE encoder made by Google. It is tuned for very high space savings at the cost of performance, but tests with ~200 files resource packs show that it is still fast enough.
 
 ## Download
-To get PackSquash, you can build it yourself, like the CI action in this repository does. Alternatively, you can get a pre-built release for 64-bit Windows, Linux and macOS systems from [here](https://github.com/ComunidadAylas/PackSquash/releases/latest).
+To get PackSquash, you can build it yourself, like the CI action in this repository does. You will also need to install both the development and runtime GStreamer libraries manually.
+
+You can get a pre-built release for 64-bit Windows, Linux and macOS systems from [here](https://github.com/ComunidadAylas/PackSquash/releases/latest).
 
 ## Usage
 ```