Document that no metadata is stripped by default

Author: tobbez

src/cli.rs

@@ -132,7 +132,9 @@ Strip metadata chunks, where <mode> is one of:
 CAUTION: 'all' will convert APNGs to standard PNGs.
 
 Note that 'bKGD', 'sBIT' and 'hIST' will be forcibly stripped if the color type or bit \
-depth is changed, regardless of any options set.",
+depth is changed, regardless of any options set.
+
+The default when --strip is not passed is to keep all metadata.",
                        DISPLAY_CHUNKS
                            .iter()
                            .map(|c| String::from_utf8_lossy(c))