Link to the Git repo directly; adjust wording.

Author: amartini51

Sources/TSPL/TSPL.docc/header.html

@@ -15,9 +15,9 @@ <h3>Important</h3>
             This is the development version of <em>The Swift Programming Language</em> book.
         </p>
         <p>
-            For the current shipping book, see <a href="https://docs.swift.org/swift-book/">swift.org</a>.
-            To contribute to its development, see the <a href="https://www.swift.org/documentation-workgroup/">Swift Documentation Workgroup</a>.
+            For the current shipping book, see <a href="https://docs.swift.org/swift-book/">Swift.org</a>.
+            To contribute to this documentation, see the <a href="https://github.com/apple/swift-book">swift-book project</a> on GitHub.
         </p>
         </aside>
     </div>
-</header>
+</header>