docs: make it clear that w3d1 doesn't require all tests to pass.

mini-lsm-book/src/week3-01-ts-key-refactor.md

@@ -16,7 +16,7 @@ cargo x copy-test --week 3 --day 1
 cargo x scheck
 ```
 
-**Note: We do not have full unit tests for this chapter. All you need to do is to make your code compile.**
+**Note: The MVCC subsystem is not fully tested until week 3 day 2. You only need to pass week 3 day 1 tests and all week 1 tests at the end of this day. Week 2 tests won't work because of compaction.**
 
 ## Task 0: Use MVCC Key Encoding