Documentation: Add static CSS file to fix tables

Add a static CSS file to remove annoying scrollbars on rst code tables.

Change-Id: I436b36fb7ee9856c7d6ad8534cd0610b7f071b17
Signed-off-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-on: https://review.coreboot.org/26263
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Philipp Deppenwiese <zaolin.daisuki@gmail.com>

Documentation/_static/theme_overrides.css

@@ -0,0 +1,19 @@
+/*
+ * Copyright 2018 Patrick Rudolph <siro@das-labor.org>
+ *
+ * licensed under CC-by 4.0
+ */
+
+/* override table width restrictions */
+@media screen and (min-width: 767px) {
+   .wy-table-responsive table td {
+      /* !important prevents the common CSS stylesheets from overriding
+         this as on RTD they are loaded after this stylesheet */
+      white-space: normal !important;
+   }
+
+   .wy-table-responsive {
+      overflow: visible !important;
+   }
+}
+