update toc for week 3+4

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

README.md

@@ -59,8 +59,8 @@ We are working on a new version of the mini-lsm tutorial that is split into 3 we
 | 2.2            | Compaction Strategy - Simple                    | ✅        | ✅            | ✅       |
 | 2.3            | Compaction Strategy - Tiered                    | ✅        | ✅            | ✅       |
 | 2.4            | Compaction Strategy - Leveled                   | ✅        | ✅            | ✅       |
-| 2.5            | Manifest                                        | ✅        | ✅            | 🚧       |
-| 2.6            | Write-Ahead Log                                 | ✅        | ✅            | 🚧       |
+| 2.5            | Manifest                                        | ✅        | ✅            | ✅       |
+| 2.6            | Write-Ahead Log                                 | ✅        | ✅            | ✅       |
 | 2.7            | Batch Write + Checksum                          |          |              |         |
 | 3.1            | Timestamp Key Encoding + New Block Format       |          |              |         |
 | 3.2            | Prefix Bloom Filter                             |          |              |         |

mini-lsm-book/src/week3-overview.md

@@ -1,3 +1,5 @@
-# Overview
+# Week 3 Overview: Multi-Version Concurrency Control
+
+In this part, you will implement MVCC over the LSM engine that you have built in the previous two weeks. We will add timestamp encoding in the keys to maintain multiple versions of a key, and change some part of the engine to ensure old data are either retained or garbage-collected based on whether there are users reading an old version.
 
 {{#include copyright.md}}

mini-lsm-book/src/week4-overview.md

@@ -1 +1,18 @@
 # The Rest of Your Life (TBD)
+
+This is an advanced part that deep dives into optimizations and applications of the LSM storage engine and will make your implementation more production-ready. We are still planning on the content, and this part will not be publicly available in near future.
+
+| Week + Chapter | Topic                                | Solution | Starter Code | Writeup |
+| -------------- | ------------------------------------ | -------- | ------------ | ------- |
+| 4.1            | Benchmarking                         |          |              |         |
+| 4.2            | Block Compression                    |          |              |         |
+| 4.3            | Trivial Move and Parallel Compaction |          |              |         |
+| 4.4            | Alternative Block Encodings          |          |              |         |
+| 4.5            | Rate Limiter and I/O Optimizations   |          |              |         |
+| 4.6            | Build Your Own Block Cache           |          |              |         |
+| 4.7            | Build Your Own SkipList              |          |              |         |
+| 4.8            | Async Engine                         |          |              |         |
+| 4.9            | Key-Value Separation                 |          |              |         |
+| 4.10           | Column Families                      |          |              |         |
+| 4.11           | Sharding                             |          |              |         |
+| 4.12           | SQL over Mini-LSM                    |          |              |         |