docs: improve wording

config/sample.engine.ini

@@ -100,6 +100,6 @@ preload_offset=15
 input_stream_retry_delay=1
 input_stream_max_retries=10
 input_stream_buffer=3.0
-# How long we have to fade in and out, when we select another mixer input (seconds))
+# Fade duration when selecting another mixer input (seconds)
 fade_in_time="1.5"
 fade_out_time="1.5"