Mark rand_os as unmaintained (#2462)

Author: jayvdb

crates/rand_os/RUSTSEC-0000-0000.md

@@ -0,0 +1,18 @@
+```toml
+[advisory]
+id = "RUSTSEC-0000-0000"
+package = "rand_os"
+date = "2025-11-17"
+url = "https://crates.io/crates/rand_os"
+informational = "unmaintained"
+
+[versions]
+patched = []
+```
+
+# and_os crate is unmaintained
+
+The `rand_os` crate is deprecated and no longer actively maintained, as `OsRng`
+is now part of `rand_core`.
+
+If you are using this crate, consider upgrading to `rand_core` 0.5.1 or higher.