Add library and deadline documentation

releases/0.5.0.md

@@ -295,9 +295,45 @@ codec, this can be enabled by removing the video_codec and audio_codec configura
 
 ### Library API Changes
 
+The library API for pict-rs has changed from 0.4. It now follows a "fluent programming" pattern of
+chaining methods to configure and launch the service from within another application. Documentation
+for the new library API can be found on [docs.rs](https://docs.rs/pict-rs)
+
+For most cases, using pict-rs' `ConfigSource` as the entrypoint is recommended.
+
+As a quick example,
+```rust
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    pict_rs::ConfigSource::memory(serde_json::json!({
+        "server": {
+            "address": "127.0.0.1:8080"
+        },
+        "repo": {
+            "type": "sled",
+            "path": "./sled-repo"
+        },
+        "store": {
+            "type": "filesystem",
+            "path": "./files"
+        }
+    }))
+    .init::<&str>(None)?
+    .run_on_localset()
+    .await?;
+
+    Ok(())
+}
+```
+
 
 ### Reject Malformed Deadlines
 
+pict-rs supports setting a request deadline with the `X-Request-Deadline` header, where the value is
+a unix timestamp in nanoseconds. In pict-rs 0.4, requests with deadlines that could not be parsed
+were treated as requests without deadlines. in pict-rs 0.5 a malformed deadline will cause the
+request to be rejected with a 400 Bad Request error.
+
 
 ### Logging Verbosity