Added some documentation strings.

Sources/EnvVars/EnvVars.swift

@@ -1,14 +1,38 @@
 import Foundation
 
+/// Holds common settings for connecting to your MQTT broker.  The default values can be used,
+/// they can be loaded from the shell environment, or from a file located in the root directory.
+///
+/// This allows us to keep sensitve settings out of the repository.
 public struct EnvVars: Codable, Equatable {
   
+  /// The current app environment.
   public var appEnv: AppEnv
+  
+  /// The MQTT host.
   public var host: String
+  
+  /// The MQTT port.
   public var port: String?
+  
+  /// The identifier to use when connecting to the MQTT broker.
   public var identifier: String
+  
+  /// The MQTT user name.
   public var userName: String?
+  
+  /// The MQTT user password.
   public var password: String?
   
+  /// Create a new ``EnvVars``
+  ///
+  /// - Parameters:
+  ///   - appEnv: The current application environment
+  ///   - host: The MQTT host.
+  ///   - port: The MQTT port.
+  ///   - identifier: The identifier to use when connecting to the MQTT broker.
+  ///   - userName: The MQTT user name to connect to the broker with.
+  ///   - password: The MQTT user password to connect to the broker with.
   public init(
     appEnv: AppEnv = .development,
     host: String = "127.0.0.1",
@@ -25,6 +49,7 @@ public struct EnvVars: Codable, Equatable {
     self.password = password
   }
   
+  /// Custom coding keys.
   private enum CodingKeys: String, CodingKey {
     case appEnv = "APP_ENV"
     case host = "MQTT_HOST"
@@ -34,6 +59,7 @@ public struct EnvVars: Codable, Equatable {
     case password = "MQTT_PASSWORD"
   }
   
+  /// Represents the different app environments.
   public enum AppEnv: String, Codable {
     case development
     case production