Add pypi metadata

auto_compressor/Cargo.toml

@@ -4,7 +4,13 @@ authors = ["William Ashton"]
 version = "0.1.0"
 edition = "2018"
 
-# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+[package.metadata.maturin]
+requires-python = ">=3.6"
+project-url = {Source = "https://github.com/matrix-org/rust-synapse-compress-state"}
+classifier = [
+    "Development Status :: 4 - Beta",
+    "Programming Language :: Rust",
+]
 
 [dependencies]
 clap = "2.33.0"