Properly specify the license in Cargo.toml. (#3)

Failed to update the `license` field in Cargo.toml, so doing it here.
(Also added the `authors` field to match our other crates.)

Author: vorporeal

Cargo.toml

@@ -1,6 +1,8 @@
 [package]
 name = "session-sharing-protocol"
 edition = "2024"
+authors = ["Warp Team <dev@warp.dev>"]
+license = "AGPL-3.0-only"
 publish = false
 
 [dependencies]