document async_std feature

Author: jbr

README.md

@@ -19,15 +19,23 @@
 ### sqlite: 
 
 ```toml
-async-sqlx-session = { version = "0.2.0", features = ["sqlite"] }
+async-sqlx-session = { version = "0.3.0", features = ["sqlite"] }
 ```
 
 ### postgres: 
 
 ```toml
-async-sqlx-session = { version = "0.2.0", features = ["pg"] }
+async-sqlx-session = { version = "0.3.0", features = ["pg"] }
 ```
 
+### Optional `async_std` feature
+
+To use the `spawn_cleanup_task` function on async-std, enable the
+`async_std` feature.
+
+```toml
+async-sqlx-session = { version = "0.3.0", features = ["pg", "async_std"] }
+```
 
 
 ## Cargo Features:

src/lib.rs

@@ -1,8 +1,35 @@
-//! # async-sqlx-session
-//!
-//! This crate currently provides two session stores: [`PostgresSessionStore`] and [`SqliteSessionStore`], each of which is enabled by a feature flag.
-//! To use `SqliteSessionStore`, enable the `sqlite` feature on this crate.
-//! To use `PostgresSessionStore`, enable the `pg` feature on this crate.
+/*!
+# async-sqlx-session
+
+This crate currently provides two session stores:
+[`PostgresSessionStore`] and [`SqliteSessionStore`], each of which
+is enabled by a feature flag.
+
+To use [`SqliteSessionStore`], enable the `sqlite` feature on this
+crate.
+
+To use [`PostgresSessionStore`], enable the `pg` feature on this
+crate.
+
+To use the `spawn_cleanup_task` function for either store on
+async-std, enable the `async_std` feature. To perform session cleanup
+intermittently with a different runtime, use a function like:
+
+```rust,ignore
+fn clean_up_intermittently(store: &SqliteSessionStore, period: Duration) {
+    let store = store.clone();
+    other_runtime::spawn(async move {
+        loop {
+            other_runtime::sleep(period).await;
+            if let Err(error) = store.cleanup().await {
+                log::error!("cleanup error: {}", error);
+            }
+        }
+    });
+}
+```
+*/
+
 #![forbid(unsafe_code, future_incompatible)]
 #![deny(
     missing_debug_implementations,