Create mmap unmaintained advisory (#1979)

Author: ppershing

crates/mmap/RUSTSEC-0000-0000.md

@@ -0,0 +1,16 @@
+```toml
+[advisory]
+id = "RUSTSEC-0000-0000"
+package = "mmap"
+date = "2024-06-10"
+url = "https://github.com/rbranson/rust-mmap"
+informational = "unmaintained"
+
+[versions]
+patched = []
+```
+
+# mmap unmaintained
+
+The `mmap` crate is unmaintained as its [repository has been archived](https://github.com/rbranson/rust-mmap) on Feb 10, 2022.
+The main alternative seems to be `memmap2` crate.