Use lowercase z for zopfli

README.md

@@ -76,7 +76,7 @@ All options are case-sensitive.
 \* Note that oxipng is not a brute-force optimizer. This means that while higher optimization levels
 are almost always better or equal to lower levels, this is not guaranteed and it is possible in
 rare circumstances that a lower level may give a marginally smaller output. Similarly, using Zopfli
-compression (`-Z`) is not guaranteed to always be better than without.
+compression (`-z`) is not guaranteed to always be better than without.
 
 ## Git integration via [pre-commit]
 

src/cli.rs

@@ -324,7 +324,8 @@ be processed successfully.")
                 .long_help("\
 Use the much slower but stronger Zopfli compressor for main compression trials. \
 Recommended use is with '-o max' and '--fast'.")
-                .short('Z')
+                .short('z')
+                .short_alias('Z') // Kept for backwards compatibility
                 .long("zopfli")
                 .action(ArgAction::SetTrue),
         )