Update polars readme with course sequence

Author: akshayka

polars/README.md

@@ -1,9 +1,32 @@
 # Learn Polars
 
+_🚧 This collection is a work in progress. Please help us add notebooks!_
+
 This collection of marimo notebooks is designed to teach you the basics of data wrangling using a Python library called Polars.
 
+**Planned notebooks.**
+
+Any notebook with the status "🚧" needs a contributor! Please file an issue if you plan to contribute.
+
+| Notebook               | Description                                                                  | Status |
+| ---------------------- | ---------------------------------------------------------------------------- | ------ |
+| Why Polars             | An introduction to Polars and its advantages over other Dataframe libraries. | ✅     |
+| Series                 | Homogenous columns of data                                                   | 🚧     |
+| DataFrames             | The central datastructure for structured data                                | 🚧     |
+| Loading data           | Loading data from various different sources                                  | 🚧     |
+| Basic operations       | Basic operations on data                                                     | 🚧     |
+| Working with columns   | Expression expansion and columns                                             | 🚧     |
+| Data types             | Basic types and casting                                                      | 🚧     |
+| Strings                | Working with strings                                                         | 🚧     |
+| Missing data           | Handling missing data                                                        | 🚧     |
+| Aggregations           | Group bys and aggregations                                                   | 🚧     |
+| Window functions       | Advanced expressions with windowing functions                                | 🚧     |
+| User-defined functions | Using custom Python operations                                               | 🚧     |
+| NumPy functions        | Applying NumPy functions to DataFrames                                       | 🚧     |
+| Lazy execution         | Lazily process queries with LazyFrames                                       | 🚧     |
+
 **Running notebooks.** To run a notebook locally, use
 
 ```bash
 uvx marimo edit <file_url>
-```
+```