Added copyright header to CSS files (#3089)

Author: Brian Vaughn

src/css/algolia.css

@@ -1,4 +1,8 @@
-/* Styles forked from Algolia */
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * Customized Algolia search result styles.
+ */
 
 .searchbox {
   display: inline-block;

src/css/reset.css

@@ -1,3 +1,7 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ */
+
 html {
   box-sizing: border-box;
   font-family: -apple-system, BlinkMacSystemFont,