un-affix top navbar

docs/_includes/nav-home.html

-<header class="navbar navbar-sm navbar-inverse navbar-fixed-top bd-navbar" role="banner">
+<header class="navbar navbar-sm navbar-inverse navbar-static-top bd-navbar" role="banner">
   <nav class="nav navbar-nav">
     <a class="nav-item nav-link" href="{{ site.baseurl }}/" onclick="ga('send', 'event', 'Navbar', 'Community links', 'Bootstrap');">Bootstrap</a>
     <a class="nav-item nav-link" href="{{ site.baseurl }}/getting-started/overview/" onclick="ga('send', 'event', 'Navbar', 'Community links', 'Docs');">Documentation</a>

docs/assets/scss/_homepage.scss

@@ -31,6 +31,7 @@
 
 .bd-navbar {
   padding: .25rem;
+  margin-bottom: 0;
   background-color: $bd-graphite;
 
   .nav-link {

docs/assets/scss/_layout.scss

-
-.bd-docs {
-  padding-top: 3.65rem;
-}
-
 // Custom container
 //
 // Doesn't use the default `.container` styles for easier modifications.