feat(book): finish overview

Signed-off-by: Alex Chi <iskyzh@gmail.com>

mini-lsm-starter/src/block.rs

@@ -0,0 +1,26 @@
+#![allow(unused_variables)] // TODO(you): remove this lint after implementing this mod
+#![allow(dead_code)] // TODO(you): remove this lint after implementing this mod
+
+mod builder;
+mod iterator;
+
+use bytes::Bytes;
+
+pub use builder::BlockBuilder;
+pub use iterator::BlockIterator;
+
+/// A block is the smallest unit of read and caching in LSM tree. It is a collection of sorted key-value pairs.
+pub struct Block {}
+
+impl Block {
+    pub fn encode(&self) -> Bytes {
+        unimplemented!()
+    }
+
+    pub fn decode(data: &[u8]) -> Self {
+        unimplemented!()
+    }
+}
+
+#[cfg(test)]
+mod tests;