Add bottom margin to tables

Fixes #45

theme/sass/style.scss

@@ -225,7 +225,7 @@ nav.subnav li {
   table {
     max-width: $p-max-width;
     padding: .5rem 0rem;
-    margin: 0 auto;
+    margin: 0 auto 1rem auto;
   }
 
   h2 {