Add more doc comments

src/lib.rs

@@ -1,6 +1,8 @@
 //! Crate for communicating with OBD-II (on-board diagnostics) interfaces on cars
 //!
-//! The high-level data retrieval functions can be found in [commands::Obd2DataRetrieval].
+//! Currently only the ELM327 is supported (many cheap USB to OBD-II devices you can buy online are
+//! compatible with the ELM327). The high-level data retrieval functions can be found in
+//! [commands::Obd2DataRetrieval].
 //!
 //! # Usage
 //! ```
@@ -14,6 +16,7 @@
 //! ```
 
 #![forbid(unsafe_code)]
+#![warn(missing_docs)]
 
 pub mod commands;