App and Environment: TraitEnvironment documentation comments

Add some doc-comments for `TraitEnvironment`.

Author: compnerd

Sources/SwiftWin32/App and Environment/TraitEnvironment.swift

@@ -1,7 +1,17 @@
 // Copyright © 2020 Saleem Abdulrasool <compnerd@compnerd.org>
 // SPDX-License-Identifier: BSD-3-Clause
 
+/// A set of methods that makes the interface environment available to your
+/// application.
 public protocol TraitEnvironment {
+  // MARK - Accessing a Trait Collection
+
+  /// The traits, such as the size class and scale factor, that describe the
+  /// current environment of the object.
   var traitCollection: TraitCollection { get }
+
+  // MARK - Responding to a Change in the Interface Environment
+
+  /// Called when the interface environment changes.
   func traitCollectionDidChange(_ previousTraitCollection: TraitCollection?)
 }