cli : Display supported formats on -vV command

Requested and inspired by patch from @ib (#771)
diff --git a/programs/.gitignore b/programs/.gitignore
index a012ce2..701830c 100644
--- a/programs/.gitignore
+++ b/programs/.gitignore
@@ -1,6 +1,7 @@
 # local binary (Makefile)
 zstd
 zstd32
+zstd4
 zstd-compress
 zstd-decompress
 zstd-frugal