doc: add haploid WF example to book (#397)

Author: molpopgen

book/src/SUMMARY.md

@@ -21,6 +21,9 @@
   - [Metadata schema](./metadata_schema.md)
 
 * [Error handling](./error_handling.md)
+
+* [Example programs](./examples.md)
+  - [Haploid Wright-Fisher simulation](./examples_haploid_wright_fisher.md)
 
 
 [Crate prelude](./prelude.md)

book/src/examples.md

@@ -0,0 +1 @@
+# Example programs <img align="right" width="73" height="45" src="https://raw.githubusercontent.com/tskit-dev/administrative/main/logos/svg/tskit-rust/Tskit_rust_logo.eps.svg">

book/src/examples_haploid_wright_fisher.md

@@ -0,0 +1,13 @@
+# Haploid Wright-Fisher simulation
+
+The following code simulates a haploid Wright-Fisher model.
+The code is a reimplementation of an example program distributed with `tskit-c`.
+
+In addition to `tskit`, the example uses:
+
+* [rand](https://crates.io/crates/rand) for random number generation.
+* [anyhow](https://crates.io/crates/anyhow) for error propagation.
+
+```rust, noplayground, ignore
+{{#include ../../examples/haploid_wright_fisher.rs:haploid_wright_fisher}}
+```

examples/haploid_wright_fisher.rs

@@ -8,6 +8,7 @@ use proptest::prelude::*;
 use rand::distributions::Distribution;
 use rand::SeedableRng;
 
+// ANCHOR: haploid_wright_fisher
 fn simulate(
     seed: u64,
     popsize: usize,
@@ -81,6 +82,7 @@ fn simulate(
 
     Ok(treeseq)
 }
+// ANCHOR_END: haploid_wright_fisher
 
 #[derive(Clone, clap::Parser)]
 struct SimParams {