RUST-478 Add connection snippet examples (#224)

Author: isabelatkinson

tests/connection_snippets.rs

@@ -0,0 +1,20 @@
+#![allow(dead_code)]
+#![allow(unused_imports)]
+#![allow(unused_variables)]
+
+extern crate mongodb;
+
+#[cfg(feature = "tokio-runtime")]
+// CONNECTION EXAMPLE STARTS HERE
+#[tokio::main]
+async fn main() -> mongodb::error::Result<()> {
+    use mongodb::{options::ClientOptions, Client};
+    let client_options = ClientOptions::parse(
+        "mongodb+srv://<username>:<password>@<cluster-url>/<dbname>?w=majority",
+    )
+    .await?;
+    let client = Client::with_options(client_options)?;
+    let database = client.database("test");
+    Ok(())
+}
+// CONNECTION EXAMPLE ENDS HERE