Update readBytesUntil.adoc

As a side note, a function readBytesTill() which also copies the supplied terminator into the array (assuming it fits) would be convenient to add as it does allow to distinguish a time-out from a termination detection.

Author: Arnold-n

Language/Functions/Communication/Serial/readBytesUntil.adoc

@@ -49,7 +49,7 @@ Data type: `size_t`.
 
 [float]
 === Notes and Warnings
-The terminator character is discarded from the serial buffer.
+The terminator character is discarded from the serial buffer, unless the return value equals `length`. If the return value is less than `length`, it cannot be determined whether this is due to a time-out or due to the detection of the supplied terminator.
 [%hardbreaks]
 
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