Add more docs for section

src/model/section.rs

@@ -1,13 +1,23 @@
+//! Data models for sprinklers sections
+//!
+//! A section represents a group of sprinkler heads actuated by a single
+//! valve. Physically controllable (or virtual) valves are handled by implementations of 
+//! [SectionInterface](../../section_interface/trait.SectionInterface.html), but the model
+//! describes a logical section and how it maps to a physical one.
+
 use crate::section_interface::SecId;
 use rusqlite::{Error as SqlError, Row as SqlRow, ToSql};
 use std::sync::Arc;
 
+/// Identifying integer type for a Section
 pub type SectionId = u32;
 
+/// A single logical section
 #[derive(Debug, Clone)]
 pub struct Section {
     pub id: SectionId,
     pub name: String,
+    /// ID number of the corresponding physical section
     pub interface_id: SecId,
 }