Add formats to manpage

man/crystal.1

@@ -361,7 +361,7 @@ Options:
 .It Fl D Ar FLAG, Fl -define= Ar FLAG
 Define a compile-time flag. This is useful to conditionally define types, methods, or commands based on flags available at compile time. The default flags are from the target triple given with --target-triple or the hosts default, if none is given.
 .It Fl f Ar FORMAT, Fl -format= Ar FORMAT
-Output format 'tree' (default) or 'flat'.
+Output format 'tree' (default), 'flat', 'dot', or 'mermaid'.
 .It Fl i Ar PATH, Fl -include= Ar PATH
 Include path in output.
 .It Fl e Ar PATH, Fl -exclude= Ar PATH