Complete comprehensive documentation for supported assets and timeframes

Co-authored-by: theshadow76 <59869868+theshadow76@users.noreply.github.com>

Author: Copilot

docs/api.html

@@ -15,6 +15,7 @@ <h1>PocketOptionAPI Async</h1>
       <a href="quickstart.html">Quickstart</a>
       <a href="api.html">API Reference</a>
       <a href="examples.html">Examples</a>
+      <a href="assets-timeframes.html">Assets & Timeframes</a>
       <a href="faq.html">FAQ</a>
     </nav>
   </header>