[Bugfix] Issue when building for watchOS platform (#14)

This PR contains the work done to fix an issue that occurred when building for *watchOS* platform, which was raised right after the release `v0.1.4`.

To provide further details about he work done:
- [x] filtered out the `CoordinatorTests` test cases and the `TestCoordinators` structs from the *watchOS* platform;
- [x] updated some texts in the `README` file.

Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Reviewed-on: #14

Tests/Coordination/Cases/Protocols/CoordinatorTests.swift

@@ -10,7 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if canImport(UIKit)
+#if canImport(UIKit) && !os(watchOS)
 import Coordination
 import UIKit
 import XCTest

Tests/Coordination/Helpers/TestCoordinators.swift

@@ -10,7 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if canImport(UIKit)
+#if canImport(UIKit) && !os(watchOS)
 import Coordination
 import UIKit