diff --git a/Cargo.toml b/Cargo.toml
index 5e30b23..e0b0a9d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,7 +7,9 @@ description = "A container that stores numbered objects. Each object can be assi
 license = "GPL-3.0-or-later OR Apache-2.0 OR MulanPSL-2.0"
 homepage = "https://github.com/arceos-org/arceos"
 repository = "https://github.com/arceos-org/flatten_objects"
-documentation = "https://arceos-org.github.io/flatten_objects"
+documentation = "https://docs.rs/flatten_objects"
+keywords = ["arceos", "data-structures"]
+categories = ["no-std", "data-structures"]
 
 [dependencies]
 bitmaps = { version = "3.2", default-features = false }
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..ba069c0
--- /dev/null
+++ b/README.md
@@ -0,0 +1,34 @@
+# flatten_objects
+
+[![Crates.io](https://img.shields.io/crates/v/flatten_objects)](https://crates.io/crates/flatten_objects)
+
+`FlattenObjects` is a container that stores numbered objects.
+
+Objects can be added to the `FlattenObjects`, a unique ID will be assigned
+to the object. The ID can be used to retrieve the object later.
+
+# Example
+
+```rust
+use flatten_objects::FlattenObjects;
+
+let mut objects = FlattenObjects::<u32, 20>::new();
+
+// Add `23` 10 times and assign them IDs from 0 to 9.
+for i in 0..=9 {
+    objects.add_at(i, 23).unwrap();
+    assert!(objects.is_assigned(i));
+}
+
+// Remove the object with ID 6.
+assert_eq!(objects.remove(6), Some(23));
+assert!(!objects.is_assigned(6));
+
+// Add `42` (the ID 6 is available now).
+let id = objects.add(42).unwrap();
+assert_eq!(id, 6);
+assert!(objects.is_assigned(id));
+assert_eq!(objects.get(id), Some(&42));
+assert_eq!(objects.remove(id), Some(42));
+assert!(!objects.is_assigned(id));
+```