Add nopCommerce integration on the website

[pavlenex]

Just like we did for SmartStore in #194 we should now add nopCommerce icon and link to the integration https://www.nopcommerce.com/en/btcpay-server-accept-bitcoin-payments

I wanted to add a link to docs instead, but I think directly linking to a marketplace is more appropriate since it has better call to actions to download plugin followed by good description.

[pavlenex]

@TChukwuleta In case you'd like to tackle it, feel free to.

[TChukwuleta]

sure. I would