Add more doc comments

src/commands/mod.rs

@@ -1,4 +1,8 @@
 //! High level OBD-II interface
+//!
+//! Retrieves data from the vehicle, over the OBD-II link. The interface is defined by SAE J1979,
+//! and a list of services and PIDs is available [on
+//! Wikipedia](https://en.wikipedia.org/wiki/OBD-II_PIDs). This module mostly uses service 1.
 
 mod implementation;
 use implementation::GetObd2Values;

src/commands/types.rs

@@ -24,9 +24,13 @@ pub struct DtcsInfo {
 /// An individual trouble code from an ECU
 #[derive(Debug)]
 pub enum Dtc {
+    /// Powertrain, represented with `'P'`
     Powertrain(u16),
+    /// Chassis, represented with `'C'`
     Chassis(u16),
+    /// Chassis, represented with `'B'`
     Body(u16),
+    /// Network, represented with `'U'` likely due to previously being the "unknown" category
     Network(u16),
 }