make rom select accept only .nes files

Author: 39bytes

web/index.html

@@ -92,7 +92,7 @@ <h2>Volume</h2>
           <div class="button-group">
             <button class="nes-button" id="nes-reset-button">Reset</button>
             <label class="nes-button" id="rom-select-label">
-              <input id="rom-select-input" type="file" />
+              <input id="rom-select-input" type="file" accept=".nes" />
               Select ROM
             </label>
           </div>