chore: include manpage for the crate

Signed-off-by: Rui Chen <[email protected]>

Cargo.toml

@@ -7,7 +7,7 @@ build = "rust/build.rs"
 categories = ["multimedia::images"]
 homepage = "https://pngquant.org"
 documentation = "https://github.com/kornelski/pngquant#readme"
-include = ["/rwpng*.[ch]", "/pngquant.c","/pngquant_opts.[ch]", "/rust/*.rs", "/COPYRIGHT", "/Cargo.toml", "/README.md"]
+include = ["/rwpng*.[ch]", "/pngquant.c","/pngquant_opts.[ch]", "/rust/*.rs", "/COPYRIGHT", "/Cargo.toml", "/README.md", "/pngquant.1"]
 keywords = ["quantization", "palette", "image", "pngquant", "compression"]
 license = "GPL-3.0-or-later"
 readme = "README.md"