Update README.md

README.md

@@ -3,7 +3,7 @@
 This script is a simple way to download a full course from Domestika.
 
 > **Warning**
-> You need to own the course you want to download. So yoi either have to have bought it or got it for "free" with your premium account.
+> You need to own the course you want to download. So you either have to have bought it or got it for "free" with your premium account.
 
 ## Installation
 
@@ -36,6 +36,8 @@ If you want to change the subtitles that will be downloaded, just put the prefer
 
 Before you can start it, you have to download N_m3u8DL-RE from here: https://github.com/nilaoda/N_m3u8DL-RE/releases. Get the lasted version binary and place it in the folder. Make sure its named corretly ("N_m3u8DL-RE.exe").
 
+Also be sure you have ffmpeg installed.
+
 After you have done that, just open a terminal and type
 
 ```bash