added Booking Travel secions

source/handbook/index.html

@@ -286,6 +286,7 @@ extra_css:
                 <h3 id="operations"><a href="/handbook/operations">Operations</a></h3>
                 <h3 id="hiring-process"><a href="/handbook/hiring">Hiring Process</a></h3>
                 <h3 id="accounting"><a href="/handbook/accounting">Accounting</a></h3>
+                <h3 id="booking travel"><a href="/handbook/booking-travel">Booking Travel</a></h3>
               </div>
             </div>
         </div>