rename RGL Synopsis to RGL API

Author: inariksit

index.html

@@ -62,7 +62,7 @@ <h3>Learn more</h3>
 
     <a href="lib/doc/synopsis/index.html" class="btn btn-primary ml-3">
       <i class="fab fa-readme mr-1"></i>
-      RGL Synopsis
+      RGL API
     </a>
   </div>