Add docblock comments where relevant

This change adds docblock comments where relevant to the code so that
it's as clear as possible without going overboard.

src/Middleware/RedirectToNewDomainMiddleware.php

@@ -15,20 +15,35 @@
 
 /**
  * RedirectToNewDomainMiddleware performs a 301 redirect the current request
- * from one domain (oldDomain) to another (newDomain) if the current request is
+ * from one domain ($oldDomain) to another ($newDomain) if the current request is
  * for the old domain. It is designed to simplify moving sites from one domain
  * to another, especially in cases where the hosting provider does not provide
  * this functionality natively.
  */
 final readonly class RedirectToNewDomainMiddleware implements MiddlewareInterface
 {
     public function __construct(
+        /**
+         * This is the host portion of the route that was originally requested, e.g., deploywithdockercompose.com, hollows.org, or rspca.org.au.
+         */
         private string $oldDomain,
+
+        /**
+         * This is the host portion of the route that the request will be redirected to, e.g., asrc.org.au, wwf.org.au, or blackdoginstitute.org.au.
+         */
         private string $newDomain,
+
+        /**
+         * If you want to perform basic instrumentation, provide this parameter.
+         */
         private ?LoggerInterface $logger = null
-    ) {
-    }
+    ) {}
 
+    /**
+     * process checks the host portion of the current request. If it matches the
+     * old domain ($oldDomain) the host is set to the new domain ($newDomain)
+     * and the user is redirected to the revised URI.
+     */
     public function process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface
     {
         $this->logger