adding logo (#45)

Author: samuelcolvin

docs/extra/tweaks.css

@@ -0,0 +1,9 @@
+/* Revert hue value to that of pre mkdocs-material v9.4.0 */
+[data-md-color-scheme="slate"] {
+  --md-hue: 230;
+  --md-default-bg-color: hsla(230, 15%, 21%, 1);
+}
+
+.hide {
+  display: none;
+}