improves style

style/bs4_book.html

@@ -91,7 +91,7 @@ <h2>Table of contents</h2>
   </main>
 
   <div class="col-md-3 col-lg-2 d-none d-md-block sidebar sidebar-chapter">
-    <h2>Note: Second Edition is under construction 🏗</h2>
+    <h2>Solutions to the Second Edition's exercises</h2>
     <!--<p>Now is a great time to provide feedback</p>-->
         <ul class="list-unstyled">
           <li><a href="https://r.geocompx.org/">Read the book <i class="fa fa-book"></i></a></li>