docs: wider docs page

Author: xmatthias

docs/stylesheets/ft.extra.css

@@ -47,3 +47,8 @@
     border-color: #afb8c1;
     box-shadow: inset 0 1px 0 rgba(175, 184, 193, 0.2);
 }
+
+.md-grid {
+    /* default is max-width: 61rem; */
+    max-width: 75rem;
+}