feat: enforce maximum width and center

src/fellchensammlung/static/fellchensammlung/css/main.scss

@@ -18,6 +18,11 @@ $confirm: hsl(133deg ,100%,calc(41% + 0%));
 
 // General Styles
 
+.content {
+    margin: auto;
+    max-width: 80em;
+}
+
 p > a {
     text-decoration: underline;
 }