misc docs

site/using/rust.md

@@ -1,7 +1,33 @@
 # Using `sqlite-vec` in Rust
 
+You can embed `sqlite-vec` into your Rust projects using the official
+[`sqlite-vec` crate](https://crates.io/crates/sqlite-vec).
+
 ```bash
 cargo add sqlite-vec
 ```
 
+The crate embeds the `sqlite-vec` C source code, and uses the
+[`cc` crate](https://crates.io/crates/sqlite-vec) to compile and statically link
+`sqlite-vec` at build-time.
+
+The `sqlite-vec` crate exposes a single function `sqlite3_vec_init`, which is
+the C entrypoint for the SQLite extension. You can "register" with your Rust
+SQLite library's `sqlite3_auto_extension()` function. Here's an example with
+`rusqlite`:
+
+```rs
+use sqlite_vec::sqlite3_vec_init;
+use rusqlite::{ffi::sqlite3_auto_extension};
+
+fn main() {
+    unsafe {
+        sqlite3_auto_extension(Some(std::mem::transmute(sqlite3_vec_init as *const ())));
+    }
+    // future database connection will now automatically include sqlite-vec functions!
+}
+```
+
+A full [`sqlite-vec` Rust demo](#TODO) is also available.
+
 ## Working with vectors in Rust