improve README

Signed-off-by: Runji Wang <[email protected]>

Author: wangrunji0408

README.md

@@ -1,3 +1,30 @@
 # SQL Optimizer Labs
 
 Build a SQL optimizer in 1000 lines of Rust using [egg](https://egraphs-good.github.io).
+
+🚧 Under construction 🚧 Stay tuned 👀
+
+## Tasks
+
+Fill the code in `src` and pass the tests in `tests`!
+
+```sh
+cargo test --test 1_language
+cargo test --test 2_rewrite
+cargo test --test 3_conditional_rewrite
+cargo test --test 4_constant_folding
+cargo test --test 5_sql_plan
+cargo test --test 6_plan_elimination
+cargo test --test 7_predicate_pushdown
+cargo test --test 8_projection_pushdown
+cargo test --test 9_agg_extraction
+cargo test --test 10_index_resolving
+```
+
+## What's Next
+
+These labs are taken from the [RisingLight] project.
+[Check out] how it works in a real database system!
+
+[RisingLight]: https://github.com/risinglightdb/risinglight
+[Check out]: https://github.com/risinglightdb/risinglight/blob/main/src/planner/mod.rs