moar structure added
- [Dataflow](./chapter_1_1.md)
- [Timestamps](./chapter_1_2.md)
- [Progress](./chapter_1_3.md)
+
+- [Building Timely Dataflows](./chapter_2.md)
+ - [Creating Inputs](./chapter_2_1.md)
+ - [Probing Outputs](./chapter_2_2.md)
+ - [Introducing Operators](./chapter_2_3.md)
+ - [Introducing Scopes](./chapter_2_4.md)
+
+- [Running Timely Dataflows](./chapter_3.md)
+
+- [Internals](./chapter_4.md)
+ - [Communication](./chapter_4_1.md)
+ - [Progress Tracking](./chapter_4_2.md)
