fix(muxing): typos (#181)

docs/advanced/muxing.md

@@ -133,7 +133,7 @@ MKVToolNix allows you to set crop values for the video stream. This is quite hel
 
 Advantages of cropping and why you should do it:
 
-- Cropping black bars allows the video to fill the entire screen. A couple of common examples would be letterboxed movies on ultrawide displays or SD content on 4:3 displays, where black bars would otherwise prevent the video from filling the entire screen
+- Cropping black bars allows the video to fill the entire screen. A couple of common examples would be letterboxed content on ultrawide displays or pillarboxed content on 4:3 displays, where black bars would otherwise prevent the video from filling the entire screen
 - On 16:9 displays where cropping would result in black bars regardless, it's still beneficial because it avoids dirty lines caused by scaling
 
 Cropping is quite simple via the MKVToolNixGUI, simply click on the video stream, go to the `Properties` tab on the right, and then navigate to the `Video Properties`.