add some basic docs

README.md

@@ -2,3 +2,39 @@
 
 A cool thing that is currently in development.
 
+## How it's structured
+
+Ideally, like RubyKoans, all exercises can be run by executing one command, in this case
+`cargo run` (most likely). This runs `src/main.rs`, which in turn runs all of the exercises.
+Each exercise is contained in a Rust file called `about_<exercise topic>.rs`. A minimal exercise looks
+somewhat like this:
+
+```rust
+fn exercise_function() {
+  "hello"
+}
+
+mod tests {
+  use super::*;
+  
+  pub fn test() {
+    verify!("REPLACE ME", exercise_function(), "Function description");
+  }
+}
+
+pub fn exec() {
+  tests::test();
+}
+```
+
+Each exercise file is supposed to have one `exec` function which gets called by the `main.rs` file.
+This function, in turn, calls all individual test functions.
+
+The tests themselves can generally be structured in whatever way is desired. Two macros are provided
+for convenience. The `verify!` macro is essentially a specialized `assert_eq!`, but it doesn't panic
+if the values mismatch, instead it prints out a helpful error message and keeps going. The
+`verify_easy!` macro is designed as a drop-in replacement for the `verify!` macro for if the learner needs help solving the exercise. It prints the expected value, too.
+
+Keep in mind that this is a very early draft of how things work. Anything here might be changed
+at any time, and this documentation should be updated accordingly.
+