add gemwallet (#165)

add Gem Wallet which currently supports BCH.
https://gemwallet.com/bitcoincash-wallet/

Author: l0vvkey

html/img/wallets/gemwallet.webp

@@ -286,6 +286,9 @@
           <div class="col-sm-6 col-md-3 vertical-align">
             <a href="https://cashaddress.org/" target="_blank"><img loading="lazy" alt="Cash Address" src="/img/wallets/cashaddress.webp"></a>
           </div>
+          <div class="col-sm-6 col-md-3 vertical-align">
+            <a href="https://gemwallet.com/" target="_blank"><img loading="lazy" alt="Gem Wallet" src="/img/wallets/gemwallet.webp"></a>
+          </div>
         </div>
       </div>
     </section>