Mark tokio-proto as deprecated (#1184)

* Mark tokio-proto as deprecated

* Note that the repo is archived

Author: saethlin

crates/tokio-proto/RUSTSEC-0000-0000.md

@@ -0,0 +1,17 @@
+```toml
+[advisory]
+id = "RUSTSEC-0000-0000"
+package = "tokio-proto"
+date = "2020-02-06"
+informational = "unmaintained"
+url = "https://github.com/tokio-rs/tokio-proto/commit/56c720ea3c74efa8f39e36c24e609628222b16a1"
+
+[versions]
+patched = []
+unaffected = []
+```
+
+# `tokio-proto` is deprecated/unmaintained
+
+The [`tokio-proto`](https://crates.io/crates/tokio-proto) crate has been deprecated, and [its GitHub repository](https://github.com/tokio-rs/tokio-proto) has been archived.
+Users may be interested in [`tokio-tower`](https://crates.io/crates/tokio-tower) instead, per https://github.com/tokio-rs/tokio/issues/118#issuecomment-452969665